So assume you're you, and your values are the same as they are here on Earth. You can be or do whatever you want in Tamriel or even on Nirn (if you think profession matters in this question), but your core values are the same.
This is from the OP. I'm not sure if some of the answers given have ignored this or if I should retract previous statements about how awesome this community is because some of the replies I've seen worry me. I mean Hircine? Sithis? Boethiah? Sanguine? Did someone say Molag fucking Bal?
No one else would choose Clavicus Vile? He is the god that can take everything you have worked for, and make you think that you've come out on top. It seriously screws with your mind, I wouldn't not to make him angry with me. I worship him, and him alone.
Not to mention, he's the Daedric counter to Zenithar, who is the one Aedra I would worship. God of Hufflepuffs, trade and communication, he is the most useful of the Aedra to worship (in my opinion, ate least) since, as I am still me in Nirn, I'm not a warrior but a simple labourer somewhere.
TL;DR: I'm torn between Nocturnal and Mephala.
Mephala, described as being a deity of secrets, and 'tact/poetic truths', has always appealed to me greatly. As much as I tend to be a gentle, pacifistic person here, if I were transplanted to Tamriel, I think I would immediately gravitate toward an assassin's guild. I loved the Morag Tong in Morrowind so much. The idea of honourable murder that pleased their goddess, on top of all of the political ramifications and manipulations of removing targets, thrilled me for some reason. I always gravitate toward any kind of assassin stuff in any media - books, games, movies, whatever - too.
I'm already very quiet and always sneak up on everyone without intending to. Imagine what I could do as an Agent of Shadow and one of Nocturnal's children? When I was around 12-13, I used to shoplift constantly. I quit, but maybe in a different world, I would've kept going and just shifted my focus away from places where people could lose their jobs because of what I'd done (salespeople get in serious trouble if they don't notice thieves). I also just really enjoyed doing the Nightingale quests and took being one very seriously.
I would probably spend my career only stealing from the houses of the rich who have more than enough. And, honestly, I'd probably distribute a fair amount of the profit that I didn't need for my own survival to people who needed help. With a slant toward people who experienced racism wherever I was, like how poorly dunmer and argonians get treated in Skyrim. I live below the federal poverty line, and I have a ton of empathy for other people who are struggling or who are treated badly.
Being an active worshiper of Boethia is a scaey prospect Manni.
Know that you are dust in the eyes of Boethiah...Worship, o faithful. Pray your death is short. Worship, o faithful. Pray your death is quiet.
And:
"Each night I pray to thee, each night I call out thy wondrous names. Surely thou must recognize the sound of my voice? Thy most devoted of believers?"
She frowned and let out a long sigh, and then of a sudden he was gone, the air from her lungs dispersing him.
What would you give to this Prince which may even come close to getting you recognition? Once recognised, what would you do for this Prince, what price are you willing to pay?
I'd pick Hermaeus Mora because the acquisition of knowledge is one of my greatest passions, if not my greatest outright, and this would be especially true in a world of magic like Nirn where the phrase "knowledge is power" is more true than ever.
I'm not too worried about the whole going insane thing because I really don't get how knowing more stuff would make you go insane. And besides: sanity is relative anyway.
There are a few other deities I'd consider, like Julianos or Mephala, but I still like the Abyssal Cephaliarch the best.