This pretty much boils down to, whether you'd like the career with a short high ramped up to 10, or would you have the longer career operating at a 3 or 4.
If you can handle the downside of a career like Nelly's, then that's the obvious choice. But a lot of people probably couldn't handle being at level 10 and then having it taken away. In which case, wanting a career like Nas makes sense, where the highs will never be as high as Nelly, but you wouldn't experience that slide down and inability to get back to an unobtainable peak.