Is Citizen Kane better than Casablanca? Is Manos better than Plan 9 [and by what criteria to you find it 'better'?]
Iron Man is a light-hearted, fun film, Batman is a dark film. Both are superhero films, but that shouldn't really mean anything: that's like comparing Tank Girl to 300.
General consensus is that Dark Knight is an amazing film, and that puts it above quite alot of films, let alone comic book ones.
BUT most people I have talked to enjoyed Iron Man, though it's firmly more of a popcorn flick than Dark Knight. Robert Downey jnr essentially carries this film, and as I said, it's pretty fun for the most part. Good effects and funny moments. Good for a laugh etc.
The 'bad guy' angle etc really isn't that flash, but luckily they don't spend a whole lot of time worrying about it.
If a girl is dragging you to Iron Man you really should be pretty happy, unless it's your little sister or something...
She could have taken you to Mamma Mia!