As a game (among other things) developer, the main reason to use SDL over SFML are:
1. A lot of money/efforts is put into it's development (Valve in particular);
2. It's apparently VERY portable (like, it is apparently easily ported to consoles);
3. It's tested and used and fixed a lot more and faster than SFML;
I remember also Laurent (maybe in pm) pointing that for serious development that needs stability, SDL is definitely less of a risk and should be the default choice. I agree with this pragmatic thinking, though I would use SFML for anything where I'm ok with the risks, just because it's far better to code with SFML than SDL.
I don't like the issues related to raw C usage so I avoid SDL as much as I can but recently I decided to replace my input library in my commercial game with SDL (the transition is not done yet though). I would have chosen SFML by default if I didn't need very long term support for that one.