I was alive during both of their zeniths (well, for part of Neil's). Although, in the interest of full disclosure, I never really got the whole "Prince is a genius" thing. Yeah, I think he's talented and has some amazing singles, but nothing on the level that the press seems to think. To my way of thinking, he's made a bunch of great singles but only one end-to-end great album. Neil Young, on the other hand, has made probably 10 albums that I would consider great.
On the other hand, Neil has CSN&Y to answer for.