D2 is better. I Quit D2 in 04 to play WoW, and recently quit WoW to come back (because D3 was announced). I was pretty much one of the best warriors and one of the best shamans around on WoW did all the raiding from pre bc MC -> Naxx, to BC up to BT/Hyjal and have always been at the top of any meters with practically every class in the game. Paying the monthly fee and stuff isn't bad, I mean I sold my first shaman for $1500 straight 2 weeks after season 1 started because I held a top 10 slot on Tichondrious, BG9 for those weeks. and sold my warrior one week after season 3 started and was probably one of the first people to have a weapon and shoulders for $800. Not bad.
WoW is just not a game you can put down when you want. You work your life around it, not the other way around. D2, you can play as casual as you like and just be a pretty good trader and know what you're doing, and you can do just fine. WoW... not so much.