Two of the more thrilling works of the 20th century came with the Miami City Ballet over the weekend: George Balanchine's "Symphony in Three Movements" and Twyla Tharp's "In the Upper Room."

Few companies could deliver credible versions of either. Even more rare are the troupes who can tackle both. But Edward Villella's sizable ensemble, with its lineup of graceful, talented athletes, managed respectable renditions, especially of the Balanchine, and here and there captured the splendor that makes these obstacle courses/poetic manifestos such triumphs.

A genuine sweetness pervades Amy Seiwert's carefree new ballet, "Soon These Two Worlds," which Smuin Ballet premiered Friday night at the Palace of Fine Arts. Perhaps it sounds dismissive to call something "sweet" these days, but Seiwert's latest is a genuinely upbeat diversion that melds solidly structured energy with a fresh, sunny disposition.

Lit with a dusky, afternoon glow by David K.H. Elliott, the six couples have the vibe of companionable friends, perhaps celebrating after a long workday - individuals make their own interpretations of Seiwert's complex steps, but everyone is dancing to the same purpose.

At a recent rehearsal, you'd hardly know Ratmansky was the next big thing. Boyish-looking at 41, his socks unraveling into his sneakers, he was still a courtly presence as he put his dancers through their paces in his new work, "Seven Sonatas."

Do it with feelings, OK?" he asks. But rather than flow together, the pathways are as complicated as traffic on the BQE. Three of the dancers crash.

It’s an appropriate choice and not only because it’s the 40th anniversary gem. This is a ballet that positively gleams with the joy of being alive. It is also fiendishly difficult, and the dancers only half coped with the snazzy inflections and jazzy insouciance conjured by Stravinsky’s Capriccio for piano and orchestra. It felt like Balanchine learnt and well-drilled rather than experienced.

But its other value as a programme starter, is that it leads perfectly into William Forsythe’s Workwithinwork, a new acquisition for Scottish, but made by the choreographer when he was still working in neo-classical mode. Set to Berio’s haunting Duetti for two violins (on record), it’s a piece that picks up where Rubies leaves off. The way the dancers stand in open-legged lines at the start, the slant of their hips later, seem specifically to recall the older piece.

Scottish Ballet is celebrating its 40th birthday. I have been following its progress for all those years, from the time of Peter Darrell's grand endeavours to establish the troupe, by way of subsequent disappointments to its present identity under Ashley Page's direction, and I do not think that the company has ever danced with greater assurance than on this visit to Sadler's Wells as the week ended.

That the repertory was created by those well-known lairds George Balanchine, William Forsythe and Krzysztof Pastor is a matter for rather less happy comment. Ballets by Darrell and by Walter Gore (who was a Scot) and a superb score by Thea Musgrave for Mary Queen of Scots were a fine reflection of national identity. But, even on this un-Scottish showing, the company is more than able to dance (if not to triumph in) Balanchine's Rubies , and to introduce a major work by William Forsythe, showing off its merits with distinction.

Krzysztof Pastor made In Light and Shadow for Dutch National Ballet nine years ago, but so well do Scottish Ballet dance it that you would think it had been made for them. Set to excerpts from Bach’s Goldberg Variations and Suite No 3 — music (well played by the Scottish Ballet Orchestra) that just begs to be danced — Pastor’s ballet for 18 begins with a handsome duet for Martin and Blyde that offers no hint of the presentational flair and rapturous elegance that follows in the ensemble work. The whole is beautifully lit by Bert Dalhuysen and has a subtle architectural set by Tatyana van Walsum.

Do you think you got in when you were too young?

I don’t think our group was. We were really in it for the ballet. We weren’t in it for the social reasons. So maybe it had something to do with the entire group, but we all had our distinct goals and encouraged each other. We didn’t do the tours that ABT II does now. It wasn’t as big of a deal; I think people stay in ABT II longer now. It’s more of its own troupe, and we were just nurtured to get into the company. We learned everything we needed to be prepared for main company life.

How different is it?

First of all there are 12 people, so you are dancing and you are dancing good stuff every time. And you get into the company and you’re standing there and it’s overwhelming because everyone’s looking at you and you’re new and you don’t know the steps and you’re going to mess it up and you’ve really got to keep the focus. That first season I think we were all in tears almost every day. [Laughs] “I messed up! They’re going to fire me!” That was rough. Then, you become part of the everyday life here. You become part of the family.

This remarkable ballerino is Meng Lu. A native of Shen Yang, China, he graduated from Liaoning Ballet School in 2000, subsequently joined that company and already boasts enough honors and awards to fill anyone's trophy shelf.

Meng's Franz exuded a purity of line, an elegance of proportion, a refinement of attack, a zest for acting, an innate musicality and such sheer delight in dancing that it struck one only occasionally that the character of this oversexed adolescent is not especially sympathetic. That's probably the fault of Arthur Saint-Léon's original 1870 choreography, adapted from an E.T.A. Hoffmann story and revised by Nahat in 1981.

First-time guest choreographer Petr Zahradnicek held to the assignment. His classically-based dessert dance, "Cake Love," began with, almost literally, the icing on the cake. Six dancers, dressed in creamy white costumes, moved with delicate showiness until, halfway through, they shed their outer clothing layers to reveal an explosion of color. One had to laugh at the sugar-sweet joy on their faces as they twirled scarves reminiscent of the smooth line of icing running through chef Jenny Dempsey's thick cake wedges.

The other choreographers looked to local flavor. Former company dancer Nicole Corea's appetizing piece, "Children of the River," was steeped in blues music. Her women are soft, supple and also tough. They flick their shins at too-forward suitors.

While their re-staging of George Balanchine's Serenade left me entranced by the graceful quality of the dancers, they missed a few details vital to Balanchine's technique. In his style, precision and an honesty of emotion is key. At times, the piece felt under-rehearsed: the allegro quality of the pointe-work dragged, the synchronicity was off, and the subtlety of the slight gestures were over-performed. The gesturing hand motif introduced at the beginning is supposed to be rather flat, but some of the dancers slipped into this loose, wiggling gesture, changing the motif entirely. We were not left wondering if the dancers were gesturing a "hello" or shielding their eyes from something. For Balanchine, it is all in the details. Nevertheless, the seductive quality of the movement was chilling, and it was an overall powerful performance.

I don't have much of an opinion about Lili, but An American In Paris and Gigi are both fascinating examples of '50s musicals. An American In Paris features Gene Kelly's long ballet finale, which is either really great or really pretentious, depending on whom you ask, and Gigi is just about the creepiest thing you will ever see passed off as a romantic story.

Creating that kind of excitement around dance is one of the festival’s great feats. The other, sometimes, is to put together unexpected combinations of dance styles and reveal new artists, companies and vocabularies of movement to seasoned dancegoers and neophytes alike.

Friday wasn’t that kind of night. The evening opened with the Australian Ballet’s production of “Le Spectre de la Rose,” the 1911 ballet by Michel Fokine that was an early sensation of Diaghilev’s Ballets Russes, this year the subject of a centenary tribute by the festival.

In 1984, with a charter and a dream, Busby began building the ballet from scratch. Starting with fewer than 30 students and no sets, costumes or props, little by little the dance company improved and expanded with Busby at the helm.

Now, they average about 50 dancers each year, several of whom go off to dance professionally, and are an honor company with the national Regional Dance America organization, in addition to putting on elaborate performances each year such as "The Nutcracker."

Choreographer Mark Godden watches the young dancers as they rehearse the opening show of the Atlanta Ballet's 80th season. Mara tucks the feather under her knee, Clark catches it between neck and shoulder, and the ballerina takes it back and flutters it like a wing. It looks light and flexible enough to be the perfect prop, but Mara notes, “You'd be surprised how hard it can be to make the feather do what you want.”

It's also hard to tell where Tamino and Pamina's budding romance stops, and where Clark and Mara's delight in their craft begins. With Godden as their de facto coach, they strive as hard as any athlete, but clearly enjoy their workout. At one point, Mara tucks up her legs as Clark hoists her onto his back, but the movement doesn't go as planned and Clark takes her on a brief, giggly piggyback ride.

Roses and Clover, a charming piece set to the music of the Puppini sisters, “is a pastiche of nostalgia, influenced by the reinterpretation by the Puppini Sisters of these beloved songs,” explains choreographer, Kirk Peterson. The Puppini Sisters is a female trio singing classical and modern songs in the style of the Andrew’s Sisters. Featured in Roses and Clover will be a mix of songs from the classic “Mister Sandman” to a reinterpretation of “I Will Survive” and the 80s hit by Blondie, “Heart of Glass.”

Baker’s Dozen, created for Twyla Tharp’s company to piano compositions by Willie “the Lion” Smith, is a work that unfolds in relaxed groupings that commence as duets and build from trio to quartets to sextets, finally arriving at dances that include the full ensemble of twelve.