I sold my keymod XCR-L with the pencil barrel to buy my SLR, and I do not regret it. My take:
If you want to customize it as you wish; SLR for sure. It's that much more of an AR-ish rifle, and I find that to be the most enjoyable part of the rifle. That, and the availability of off the shelf parts should I ever need them. Spare parts for the XCR were XCR specific and less plentiful and more expensive
If you want an out of the box rifle that you don't need to mess with, the XCR-L is a solid choice. Aside from the side charging handle, I could argue that the ergonomics on the XCR are actually better thanks to the bolt catch/release tabs from the factory; it seems like a small thing, but it really was the icing on the cake for that rifle.
In the end, my familiarity and desire to have an AR clone is what led me to my SLR, but you can't really go wrong either way.