Took a long time deciding between these two Black Book powers... Went with Black Market as the trader carries Daedric weapons and armor that can be purchased... How awesome of a power is this though?

It depends. I know the servant can carry a bunch of stuff and can be cast multiple times a day so I went with him. Can the merchant be summoned more than once a day? If he can only offer you 2000 gold worth of trading a day I would definitely go with the servant.

Plus, you have a Daedra for a BUTLER.

The Deadric Butler Power is a Lesser Power, so it can be used as many times as you like. Same with the Deadric Trader.

The trader seems to take a while to recharge before you can summon him again though. I went with the butler (as I was lugging loads of bones around from doing the MQ). He could hold most things, but he quickly reached his weight limit.

yeah the butler seems to have like a 200-250 weight limit. but hey he's always wanted to be a pack mule right?

He's so polite for a Dremora

I tested and summoned both, and it seems multiple times a day... I've only done 2 Black Book quests and I'm liking the powers they grant... This helps a ton with long dungeon crawls especially in this DLC where I seem to want to pick up everything