I personally prefer Extremis. IMHO, Extremis was the last armor that really showed a solid Iron Man armor. It's not that I don't like this one but the name Iron Man entails something metallic and hard when it comes to the design--and the fact that it was designed to be exactly that and, at the same time, be technologically adaptable really got my vote.
This has to be Tony Stark's most powerful suit (That wasn't increased in power by an outside source such as the Thorbuster etc.) Grant it he used Mr. Lametastic's lab he built everything with his own genious and ingenuity.