before surgery, I mostly did water aerobics and "rode" the stationary bikes at my gym. Two hundred pounds later, I still do those, but i also bike a lot, too, now - in fact, I bike four or five days a week except in the winter. I also do Zumba occasionally.
exercise isn't going to have much effect on your loose skin. You may get some more muscle definition if you do some strength training, but if you've got a lot of loose skin, it's not going to look A LOT better, even with that.