I have come to the conclusion over much agonising that Iron Man is the better film, but Iron Man 2 is more enjoyable, that is however, not to say that Iron Man 2 is not a great film too, or that Iron Man is not enjoyable.
In plain english for people who don't get my scatter-brained logic. I think Iron Man is generally more coherent and has a much more logical plot and tighter pacing, but Iron Man 2 was more "fun" and had a bigger cast with a lot of great actors. However, Iron Man 2 IMO was still a good film, I think the plots tied together well and it had a lot of great moments.
I feel I have to say I think IM2 is still a legitimately good movie because I do like, and sometimes love, some movies that are clearly not cinematic masterpieces, but I still love them to bits. Transformers 2 for example. I know lots of people think it's a travesty and I wouldn't dare say it's a movie that is particularly "good" in the critical sense, but I still enjoyed the hell out of it.
Tl;dr version: Iron Man 1 is a good film, Iron Man 2 is better entertainment