If it were me, I'd say standard 4:3, 30i NTSC (or 25i PAL) to take advantage of a good, lightweight, all-purpose camera that's really good in low light, like the PD-150.

Lots of wild, obscure and crazy things going on in and around a convention -- much of which (behind the scenes, the protestors outside, -- who knows, maybe a jail cell?) may not be particularly well- lit.

You want flexibility here to shoot any kind of situation that comes up in a quick moving "run 'n' gun" scenario, not necessarily one set "artistic" look. Try to get the best useable footage you can, and worry about niceties like aspect ratio and progressive scan in post-production.