I'd go for sleep, just to be original. If we could do without sleep, it would leave more hours in the day to do...whatever it is you would want to do with an extra 8 or so hours in the day. Plus, you would save money on things like beds, alarm clocks and the like.
Funny, I've on occassion talked to people about what it might be like if we could do without sleep, something to which they always respond "oh, but we need sleep, you couldn't do without that"!
Seems the same has occured in this topic, they seem to totally miss the part where you said the scenario was that you just didn't need sleep, full stop.