I just thought I'd jump in since no one else had used sfml and throw my vote in for that I found it extremely easy to use and get familiar with. Personally, I'd suggest trying out both and seeing which you're more comfortable with. I had some issues with SDL(though it's been awhile and don't recall what ) and ended up with sfml. I never had any problems with it and was extremely pleased with the library overall.
I think the SFML vs SDL question is one of those entirely subjective questions, unless you're asking for a very specific reason or need a very specific thing from your library. They both have their pros and cons and you'll alwyas get 10 different answers from 10 different people. So, unless you had specific requirements of your library, I'd suggest flipping a coin, or even better, just installing both and seeing which tickles your fancy
As mentioned above, opengl isn't recommended or necessary for simple 2D games. There are things you could use it for, but as someone who is currently learning opengl, I suggest staying the hell away from it for awhile until you're really comfortable with making 2D games. It's taken years off my life
Edited by Misantes, 01 June 2014 - 12:22 PM.