Re: Favorite villain of the trilogy?
The Mandarin. And by 'The Mandarin', I mean Aldrich Killian, who, despite being an amalgamation of different characters (Killian, Mallen - that's why he breathes fire - and Mandarin), does end up being the final threat that Tony has to face against in the movie.
And believe it or not, I voted for Killian thanks to the twist. Well, if the Mandarin seen in the TV broadcasts was the real threat, then perhaps we'd get an all-out straight battle between Good vs. Evil. With the twist, though, we got a...well, twisted and complex plot, involving a man who creates a diverting villain persona, ignites a full-scaled war under that same persona, and eventually takes advantage of all his actions under that persona for his own - all the while he keeps a personal vendetta toward the main protagonist. So yeah, I'd say it is more interesting - albeit less like the comic book typicality, which could also be a whole 'nother intriguing approach - but each to his own.
As I already said, Obadiah Stane was awesome (mainly thanks to Jeff Bridges), but I always saw him as a bit too conventional. Vanko was little more than a plot device, getting no development or even characterization; Hammer was funny but I never considered him a real villain. Raza was awesome though, I would have liked to see him in the poll and I would venture to suggest that he was an even more serious character than Stane.
If crossover villains counted though, Loki would win against any of these guys (not talking about strengh here, but about general character construction). Like easily, Hiddleston plus Whedon writing will do that to you.