Does anyone still play NES ? Really ? I prefer DS, you can take it wherever you go and the games you can play with are those of my childhood (Pokemon, Mario Kart, etc.)
The NES can't really be compared to the DS, since one was released, like, 15 years before the other, so the games' quality has increased dramatically for the DS when compared to the NES, and, on top of that, DS is portable and can support games from the GBA, which is why I'd have to go with it. (Plus it's the only handheld I've had and I have a lot of good memories with it, so)
Like Chehov said, you can't compare systems like that as they are from two completely different time periods. But to answer your question, I'd rather the NES.