Best Legends toy... any repaint of the Cybertron Starscream. Nice articulation for a Legend, same transformation as the larger versions, and even has the gimmick intact. Some of the Universe 2.0 Legends are a close second, Megatron, Jazz, Cosmos, Animated Bumblebee, and Brawn are all great.
I'd have to go with Universe Legends Bumblebee. The transformation is fun, and the rendition is really well done. Close runners up would be Animated Prime (just wish he had knees), RotF Jetfire (love the leg transformation) and Cybertron Starscream (for reasons already mentioned).
I really like the Cybertron Starscream mold and any of its repaints. G1 Brawn, Beachcomber and Bumblebee are also very nice.
Universe Legends Warpath, Cosmos, Jazz, Hound, Beachcomber, Wheelie, Brawn, Bumblebee, and "G2" Megatron are all winners.
I give serious credit to Legends that are in scale with their chacters, not just funky little versions of bigger guys... So, as others have said, I gotta go with the Universe 2.0 Legends, especially those of G1 mini-bots. Seriously- every time I look at them on the shelf I'm pumped that they made Brawn, Wheelie, Cosmos, Warpath, and Beachcomber done more or less in scale...
Legends Movie Springer. Not because of his articulation (He has none) Not because he's a stellar update of an existing character (He's not) But because he trumps the Voyager-class bot with the same alt mode. Seriously... hands AND better proportions AND doesn't have half the alt mode hanging off his back. Suck that, Incinerator!
This is a tough one. I'll go with Animated Bumblebee. He looks great (my favorite mold of his character) and is in pretty good scale with a lot of my Animated deluxe, voyager and leader figures.
Hot Spot (or whatever they're calling him now). Legends Prime is cool enough, but looks badass in the homage deco.