GLFW just goes from zero to OpenGL context ASAP, plus input events. With SDL I found that their drawing primitives are too limiting for my needs, and if you want to do any custom drawing at all, you need to abandon their drawing primitives entirely and just write GL codel. At that point, GLFW makes more sense.
SDL does have a few other nice things like audio support and text rendering, which you'd have to figure out separately with GLFW, but to each their own.