I couldn't decide between Izumi and Ed at first but I still went for Ed. I just see a lot of potential in him. Sure he does alchemy w/a a transmutation circle coz he's seen the gate but I still think that's big for someone so young. Beside he uses his alchemy in a smart way, not all ppl can do that. Oh I think Al's alchemy rocks too (it's pretty much the same as Ed's at least in the manga
Roy's is cool but it just doesn't impress me that much seing flame magic all the time in anime, movies, books etc. Plus his weakness is also a negative factor.