Neither of them are really much like O'Neill, by Mitchell really is far more. He likes all the stuff blowing up, is kinda dense sometimes, etc. Sheppard generally tries to calm down the people who get overexcited about some new thing (unless 'some new thing' is an Ancient toy, then he has fun with it) I do like Sheppard better than Mitchell, too.
Mitchell isn't an O'Neill knockoff, though--he's Jack if he'd grown up about twenty years later. Fairly different, though there are similarities.
I think Rodney is less concerned about the universes that won out than his sister telling people his
real first name.