Yeah, but we really haven't seen them fight and they weren't really the Emperor's personal bodyguards, they were just Coruscant security. They just happened to travel with him because they were the best other then the 501st who were reserved for Darth Vader. I say it's close but Vader's Fist triumphs.
Well here's where experience comes in to play. The rent-a-cops (just cause you called them security) that surrounded Palpatine weren't battle-hardened and battle tested. Especially not to the caliber of the 501st. The Emperor took special interest in the 501st due to all their success and victory record. They acted more as law enforcement with a little extra brutality thrown in there. They were never designed to be a deployable army, although they were the first to don the name "stormtroopers."