I didn't learn AS2, but my general impression was that AS3 is much deeper and more versatile, so if you want to keep learning and make more advanced stuff, choose that! The old Actionscript 2 is simpler, so it's probably easier to learn. More limited in what you can do though, and maybe harder to find tutorials for, since it's old.
No problem and good luck!!
Wish I could give some more specific advice, but it's been a while ^^'