It was a rhetorical question. My answer is "worse enemy."
Your best friend would blow your head up, expanding an already inflated ego. Then when sh*t hit the fan, they would pee on the ground and desert you, leaving you a-lone. But the advantage of having your worse enemy would be, you would be en Garde all day, so when the worse thing happened you would respond with the appropriate defensive tactic and not over-step or under-step your bounds, possibly saving your own (corporate) life.
Just wanted to get this tidbit in before the close of the first break. Have a good day.