Yeah the thread was here not so long ago. However, it can be pretty much summarized by saying that SFML is written in C++ in a very object oriented fashion in the traditional sense of the term while SDL is a C library and the API is thus purely procedural. So if you prefer one of these over the other, there you go. But honestly if you're just beginning game development and just want to make some games, the choice really doesn't matter except that SFMLs API may be a bit more friendly looking to you. Just pick one and play around with it, if you don't like it then you can just switch.
Thanks! And sorry about the new thread thing, I didn't find it for my quick minute of searching.