prefinished or unfinished?   
we always used tar paper (roofing felt) under hardwood   
my experience with the prefinished is that it chips and knicks easy, but once its down your done clean up the mess and move on   
with unfinshed you can fix mistakes easier but you'll need to sand and finish it after it installed we always contracted out the finish part one wrong swoop with that sander and all your hard work goes down the drain   you'll have extra time in it this way 2 days sanding and probably another week to put the finish on the floor and have it hard cure     
you can't go wrong it looks nice either way