The SL is geared towards all-mountain riders. Most people on this forum adore the SL and have nothing but great things to say about it. I myself am in the process of buying one, so I have no actual experience with the board. If you plan on getting into jibbing/rails you might want to look elsewhere.
The Evo is more of a park-oriented board, if you see yourself spending a lot of time there it could be a solid choice. Won't handle as well all over the mountain but I'm sure it's not that bad, especially for the average rider.