I recently got a 2013 KTM 150 XC for my son and, while braking it in, loved it so much that I had to have one as well, but the only deal I found was for a 2014.
I have only ridden four strokes before, starting with a CRF 150, 250 WR and the Husaberg 390. Switching to the light and nimble two strokes was a blast.
The differences that I can see between the 2014 and 2013 are:
In fact, the 2014 is setup so poorly from the factory that if I had bought the 2014 first, I would not have bought another one. The 2013 is sweet as corn right form factory.
The 2014 jetting is richer at the bottom and leaner at the top.
These are very light machines. In fact 40 something lbs lighter than my Husaberg 390. There is sufficient power of the bottom to cruise around and lots of power on the top. I was surprised by how much power there is at low throttle openings. I weigh 150 lbs and during break-in, it was enough in the first half throttle to keep my smiling and exploring the handling.
I expected to have to rev the thing all the time to keep it going, but the only thing you need to keep it revving for is the smile.
The 2014 is really poorly setup from the factory. I took it riding 4 times and it fouled three plugs while just warming up. I have now dropped the jetting to the 2013 spec and I'll have to see.
I am still adjusting the 2014 to match the other one. It is poor in every way, I don't know if the 2013 has different power valve settings, but it runs much better.
I'll let you know what settings I end up using. For now:
Update I figured out why the difference. The 2014 uses a different, much cheaper power valve, from the factory: they no longer put the nice VForce in there, but some junk.
Read the detailed impression in the FE 390 vs 150 XC comparison: KTM 150 XC vs Husaberg FE 390.
Here are some more links related to the 150s: