IMO, in a ranked setting Smash is the better spec. Smash can hit up to 5 targets and if for some reason your team gets pushed into a corner (voidstar) or if your team just happen to be in range of the smasher it can do up to 35k+ dmg all together which doesn't include damage from the other 5 dps/tanks on your team.
Carnage IMO, is the more enjoyable to spec to play in regs/rwz. The amount of control you bring to single targets, the constant predation, and the single target burst (especially when white barred) is unmatched. Unfortunately due to my 300-400 ping i'm forced to play rage most of the time. But I do still think that carnage is viable but maybe not as effective.