I've got the MVM belt drive on my 15 PC. I haven't tried any of the others, so I have no experience with them, but I do know that I've put some hard hours and miles on the MVM and literally have had ZERO issues.
The drive performs exactly as described. There is a noticeable difference in performance and engine acceleration between a stocker with a chain case compared to the belt drive. This was one of the first things I was interested in testing when I got mine. Two 15 PC 800's, one with the chain case and one with MVM belt drive. Both riders I was with had the chance to try them out for comparison and both came back with the same feedback.
One of the things I appreciate the most out of the MVM belt drive, is the quality and craftsmanship of work. I had the chance to meet and ride with Dean from MVM and picked his brain a bit about the machining process, tooling, programing, etc. If I remember right, everything is machined from 6061-T6 aluminum.
Regardless of the direction you decide to take, you won't be disappointed by making the upgrade. I am just speaking from my personal experience that I have had with Dean at MVM and I know for a fact that if I ever did have a problem, he would be right there to make sure I have a solution immediately. Customer service can sometimes lack in the snowmobile industry and so many people get frustrated with bad dealers, vendors, etc. It is nice having a company step up and back their product 100% without having to worry about all the BS.
If you want, give Dean a call at MVM and run your questions by him. He can pretty much answer and give you a good idea as to what the install requires and anything else to do with their product!
MVM Motorsports
Dean Harris (435) 563-3632