Best what? Yeah, we didn't know what one was, either?until we saw the latest Teatro ZinZanni production, Maestro's Menagerie. Now we know that an equilibrist performs difficult feats of balancing, and we're confident that nobody in town does it more beautifully than Elena Borodina. For most of the show, this Russian gymnast plays an arch sidekick to the Maestro himself, her curly blonde hair pulled tightly back in a bun. But eventually she emerges atop a piano, her hair loose and tousled, her lithe figure shown to full effect in a revealing bodysuit. She then proceeds to stand on her hands?and often, just one hand or the other?all the while moving her legs into artful positions that are accented with a long, white scarf flowing around her. It's a show-stopping moment of strength, grace, and sensuousness, and quite likely the best equilibrist performance you'll see this, or any, season. ?Nina Shapiro 222 Mercer St., 802-0015, dreams.zinzanni.org