It's going to depend on your riding area which will work best for you. If it's tight trails then I would go xc, if machine width is not a concern then I would go "S". As for the differences as RZR_Scott said above the biggest is going to be suspension. The 2010 "S" has 12" of travel front and rear and is 60" wide( actually will measure 62ish with stock wheels) has Fox Podium 1.5 shocks, integrated rear cage(back bones), different style front grill and hood, 39 psi fuel pump, bigger cv joints on the axles and no power steering from the factory. Now this is based on a stock machine, who know what may have been changed in 2800 miles. And power steering can be added for around $500 and I highly recommend it. Now for the 2014 XC, it has 9" of front suspension travel and 9.5" of rear suspension travel and is 55" wide ( probably 57ish if measured) with the stock 14" high offset wheels. It basically a stock 50" 800 suspension set up with better shocks and high offset wheels to make it wider. It prolly comes with oem power steering, and perhaps some other special add ons from factory that no other rzr has. Has the updated 2011-14 front grill and hood. It also should have the 58 psi fuel pump that came in the xp900's. Also does not have the integrated rear cage(back bones) those were only offered on the 2009-2010 "S" models. And probably a few other differences between them but those are the ones off the top of my head.