I own a MKI and a bull barrel MKIII and have fired pretty much every iteration. I prefer the MKII slightly over the MKIII, given a choice. Depending on where and at what range you will be shooting, I suggest giving both the fluted and bull barrel a try to see what works better for you.
I'm a big fan of the MK series as a target pistol. It's extremely well made for the price, accurate, and there's a wide range of sights and accessories available. Just for kicks, I installed Crimson Trace grips on mine and they've been fun, if not particularly useful.
The only negative about this firearm is cleaning. The MK series is a pain the butt to tear down and reassemble (for me, it involves fingernails, bent paperclips, and time). However, I have never had a misfire, even with a thousand rounds between a thorough cleaning.