Anyway a lot depends on your budget. You can spend as little as $2,500 to $30,000 on a mtn sled. If money is tight I would try find a clean Ski Doo Rev Summit chassis with at least a 144 inch track. Polaris RMK's are good but the newer the better & stay far away from the 900cc model, junk. Arctic Cat has come long way in dependability but still seem to have ways to go. The M series sleds are very light but not as bullet proof as say a Rev.
If it was my money I would get a used 2008 Polaris RMK 600 with 144 track. Good power, easy to maneuver in tight spots & can jump it.