my main toon is a dual wield mage / magic. and when i got the nightengale armor i got rid of half my magika regen armor for it, cuz the nightengale armor is EPIC, along with that baaaadaass nightengale bow. my god it badass looking. It about as epic looking as my rogues bow on Rift from the Hammerknel Fortress raid

I haven't done the thieves guild yet, but the Dark Brotherhood is really fun.

The Thieve's Guild is a bunch of punks who live in an Attaxia-ridden sewer.
The Brotherhood has much cooler gear, too.
But I would play both, as it would be repetitive to make 2 characters for each faction.

I found the DB quests very disappointing, lacking the imagination of the Oblivion quests like Summitmist Manor, the assassination in Bravil etc. The Thieves Guild on the other hand was fantastic, and although the Nightingale part should have been expanded on, the end game of the actual Thieves Guild is really good.

I really hope somebody decides to release a Nightingale quest mod though. Would be fanastic in an area ripe for building on.

Funny I had the same feeling about the DB quests, it lacked the depth and careful thinking through that I enjoyed in the Oblivion DB quests. Nothing like the Manor killing where you had to follow the guy and figure out the exact time to best put the drop on him (literally).

It's the Black Sacrament, not the Dark Sacrament.


Speaking of which, is it weird that I've accidentally memorized it?

I'd say if you want to do one at a time. Start with Thieves guild.