The Sheik was an innovator, and considerably less sloppy than his nephew when it came to in ring work. He was capable of having decent matches with old school performers like Bruno Sammartino, but also of having the first ever hardcore brawls. I believe he even had a run in ECW in his 70s, but I haven't seen any of that, and can't imagine it's that good.
Sid is dogshit, and in a match-up of intelligence, wrestling technique or general qualities of humanity, he'd lose. However, it is a wrestling match, and Sid's dominant power would mean that he'd pick up the win here, as long as he doesn't go to the top rope.