It's a common mistake to confuse the two. His hair is a little longer, more rigid, and instead of 4-5 bangs coming down it's 3 with gaps inbetween them. Or it can be one large bang in the center and 2 tiny bangs on each side with gaps that divide them from the center one. It was drawn those two ways in the Buu saga.
You see a lot more forehead with SS2 Goku, Gohan.
I'd buy a Super Sayian 2 Goku! It would be cool if bandai makes him with that confident smile