Deidara, definitely. For one, I love his explosions. Two, he seems like a guy you could have a nice chat with as long as you don't insult his art. He's usually serious, but not as serious as, let's say, Kakuzu or Itachi. Kakuzu obviously hates talking, and I'm pretty sure his explosive temper would be the death of me at some point. He did kill all his previous partners.
Trying to talk to Itachi would just be... awkward, considering I know the truth and stuff. I'd probably be nervous the entire time -.- But, if I somehow got over it, I wouldn't mind hanging out with him. I can be quiet for a very long time if I want to.
Tobi would scare the crap out of me, knowing what I know now. Even if he was acting goofy, I'd be on my guard 24/7.
Kisame is kind of intimidating as well, but I'd get along with him too, I think. At least, he doesn't seem like the guy who'd randomly chop your head off for something you said.
Hidan, well, as long as I keep my mouth shut about religion and let him do his thing, I figure it would be hilarious to hang around him, but he's still a bloodthirsty maniac.
Konan and Pain are way too serious, Zetsu is a definite no-go, Sasori is a jerk, I don't like him >_>
So my ideal choice would be Dei! <3
After Dei, in order, Itachi - Kisame - Hidan (for teh lulz)