MY GUESSES FOR MWC:
Star of the Show: 3D LG Phone. I'm guessing (or hoping!) it will be similarly spec'd to the Optimus 2X, except it will have the better Tegra 2 SoC, the 3D one.
I think this phone will not only be revealed, but have working units for the press to play around with.
Runner up / Arguably the Star of the Show: Galaxy S2. It was the king of 2010 sales; samsung will definitely have thrown tons and tons up R&D funds at it. It will be announced, with specs, maybe a live demo, etc, but I do not think it will be available on the floor to play around with (which is why I think the 3D LG might get more press).
I know samsung bought up tons of tegra 2 chips for nvidia, but I think those are bound for the galaxy tab. The Galaxy S2 will, I think, ship with Orion (which is why I don't think it will be ready to show off; the Orion was just shown off like three months or something ago, so I think it's kinda far from mass production, but I bet they have working prototypes).
HTC will get good press for maybe 3 - 5 phones, a couple of which will be dual core and look really terrific. Verizon needs some love, so I'm guessing maybe some Verizon exclusivity of the best dual core phone?
Moto will announce some midrange/feature phones, and also continue to talk up the webtop / docking system stuff the Atrix (and maybe eventually bionic) will be able to do. Maybe officially say the release date?
Only guesses, could be very wrong!