Sonic 1 is pretty okay.
My absolute favorite version is the arcade release that adds a shorter time limit to each stage and cuts out Marble, Labyrinth, and Scrap Brain 3. In a very real sense, those levels just aren't up to arcade-spec. Scrap Brain 3 is obnoxious, who the FUCK decided that there needed to be a fourth act of Labyrinth?

the last boss is very dumb in S1, and I think it otherwise has MUCH better bosses than the entire rest of the franchise (S2's bosses all suck ass, but you can at least cheese all of them)
but the Final Zone boss is just ass