I kinda like celestial. It´s fantastic in campaigns with lots of undead and could double as a healer.
Also having a Unicorn as a patron gives room for a lot of jokes.
YES. I want Celestial pretty badly because of that sexy magical multitool vibe, and unicorns are awesome. The very thought of having a unicorn as a patron makes me feel a little horny. (You were right about the jokes!) If there isn't one, well... second choice might be the archfey
Lurue, because she's kind of horny herself.
I'm curious how Celestial or Archfey warlocks would fare against mind flayers. GOO should be better in that regard, but I read the list of GOOs and the more I think about it, the less I want to get any GOO on my good PC after all. Seems about as terrible an idea as a deal with a devil, if way cooler and creepier, and smarter (sorry, Wyll!) because you're dealing with something that is hopefully not as close by and hopefully will never break through into your dimension. Hopefully. Since they all kind of sound like variations of Azathoth. Too bad none of those would really fit well with a dwarf like boring old Fiend would (sorry, Wyll!), but I'm still leaning towards a suboptimal dwarven warlock with rolled stats at this time.
Anyway, Celestial and Archfey are currently my favorites for sure, though Lurker also sounds fun. If all three were in, I'd probably do them all, since I'm such a warlock fiend... okay, that's two puns in one post, I'm officially going to hell, and not even because of a pact.