Honestly man, it's a matter of preference. So many variables, the most important being your own ears. These are all fairly common speakers, I bet if you go to your local music retailer (Guitar Center, whatever) you'll find them set up so you can demo them. Personally, I own the MKII's and like em quite a bit. Very precise. However, the guy I talked to preferred the HS80M's, he just liked the rounder low end. I personally didn't care for KRK's stuff too much.
Notice all the use of the word "personally" there, lol. Just go check em out and see what you think