It totally depends on the focused hardware you intend it to be played on.
But for sake of "simpleness", and ease of programming, I'd use SDL2. Sonic styled games are mostly a 2D platform/adventure games, so then unless you'd like to use Pixel Shaders and all that fancy (and useless IMO), graphical effects in excess, I'd use SDL2.
If you intend to make a Klonoa styled game themed as Sonic, then you might use OpenGL.
Do you have any graphics style idea beforehand?