Originally Posted by cherokeesam
He can do both in the comics, too. He just prefers the BIG version of Pym because giants are strong and powerful and very, very visible.
Personally, I think the ideal balance for the movies is just to make Pym Giant-Man and Janet Van Dyne Wasp, and then forget about the character of Ant-Man (Lang or Pym) altogether. It's simply a question of powersets: make Hank the grower, and Janet the shrinker. If you add Lang as Ant-Man, or make Pym Ant-Man, then you create a redundancy: why have *two* --- or even three --- shrinkers?
Well it's only Lang who creates a redundancy. Jan, simply by being Pym's gf and then wife, would provide reasons why he might want her to have a similar powerset, so she can accompany him on his adventures. But even if that isn't the reason, size changing is Pym's speciality anyway. He gave Janet similar powers because that's the field in which he is an expert. He might want to occasionally shrink down himself so HE can accompany her and they can work as a couple. I don't think that, just because Pym becomes Giant Man, that he can't ever shrink down to ant size.
Besides, Pym and Jan's powers aren't exactly the same when shrunk down anyway. Pym uses size changing as more of a surprise tactic, and controls ants. Jan tends to stay at insect size and uses her bio stinger. So Jan's powers are more similar to Yellow Jacket's than Ant-Man's, although really YJ's is actually a combination of Ant-Man and Wasp.