Don’t get it mistaken, Silver Surfer is especially powerful and capable of wiping the floor with the likes of Superman. Thanos is just on another level.

The problem with cosmic-level entities is that power scaling is difficult to fathom. In his current/most popular incarnation (All-Star Superman), Superman is capable of pushing the Earth out of orbit, and that's without over-exerting himself. That's saying nothing of Golden Superman, who can snuff out a star with his cold breath like we snuff out a birthday candle.

I would put him below people that can blink reality out of existence like the Beyonder, but he could stand toe-to-toe with any of the Marvel bigs like Galactus, Thor, Hulk, SS, etc.