The best way (and way to not get the Tops to hate you as a whole) in my opinion is in his suite. You'll need either Black Widow on a female character or 60 Speech to get him up there alone. When your conversation is over, quickly sneak (Stealth Boy if necessary) and use a weapon like a shotgun that will one-shot him from sneak. If you kill him before the four thugs come up, they won't be hostile and you can leave as if nothing happened.
Alternatively, talk to Swank at the front desk. If you got a smooth tongue (speech skill) and a few pieces of evidence on your side, he'll arrange for Benny to meet you alone in his suite, with all your weapons. Then you can take him out at your leisure.
XBL Gamertag: Mister Morn But our Morn is in another castle!
If you have a female character with Black Widow you can sweet talk him to get him in his suite. Then you can either just attack him there and kill him or sleep with him first and kill him in his sleep which you can do without actually having to fight him.
My power is discombobulatingly devastating. I could feel his muscle tissues collapse under my force. It's ludicrous these mortals even attempt to enter my realm