Cross on left
Pros: Enables look ahead.
Cons: None really. It is a good compromise between cross on top and bottom. Having said that, not many people make a cross on the left, possibly because the fingertricks are not that good for this variation.
Cross on bottom
Pros: Enables great lookahead, and also decent fingertricks. Most of the really good speedcubers solve the cross on bottom, and so should you.
Cons: It may be a little akward for beginners at first because you cannot see your progress with the edges, and it is also hard to see if you accidentally screwed up. And if you do, it is guaranteed to be a huge setback.
I only know one person who solves cross on left. most speedcubers are more comfortable solving it on bottom.