I just went through this! Let me share my findings.
The Mark 2 has two top bolts per ring - one on each side. This did not impress me as very stable. I looked at it in person, and it had a less than solid feel to it. (I had just spent $1,000 bucks on a Leupold scope, so I wanted something rock solid to hold it.)
I then looked at the better Mark 4. (I have Mark 4 rings on a different rifle, ther are great rings) But the Mark 4 comes in two pieces - a base and an upper. Together, they are over $200.00 dollars, and are still two pieces. I wanted a mount milled from one piece of metal.
I checked out the LaRue LT104. This mount has an amazing reputation. So, I bought it directly from LaRue. I mounted my scope, and went to the range. I was 3MOA high and 3MOA right the first time I pulled the trigger. The scope hadn't even been bore sighted, and not only was I on paper, but was close!!! A few clicks later, I put 5 shots within an inch of the bullseye.
Larue included a couple cool swag items with my order too. But the rings were the star of the show. Spend once, cry once has never been more true. Good luck!!
EDIT: I also recommend the BCM Gunfighter Mod 3 Charging Handle (about $50.00). It allows you to easily charge the weapon no matter where the scope ends up.)