My one brother owns a 2008 700 grizzly and loves it.
My other brother owns a 2009 AC 700 mud pro and loves it.
Neither has had any problems.
I have a 2010 700 mud pro,but I haven't driven it enough yet to give a honest long term opinion yet.
None of these are diesel, however my brother spent a lot of money on larger tires, clutch kit etc, which are stock on the mud pro.
I think the front snorkel could be designed better as it interferes too much with front storage.
Here is some good information
Arctic Cat - ATV Nation