Kabuto or Orochimaru

Because they do extensive research. I'm interested.
I may most probably end up being a human subject (no one escapes Orochimaru T.T) but well, if it makes me powerful and he guarantees that I won't be killed (as if xD), then I'm fine with it.

But, I would beat him to it by using him first as a subject, before he gets to me xD

Orochimaru's experienced and pretty merciless ... and old lol. Doubt you can outdo him. He doesn't mind killing humans either ... dangerous, man. Oh, and he ain't a human ... you don't know what you're gonna expect if you use him as a subject, he might just come up with this unexpected kinjutsu and then BAM. You dead Dx

Minato! Forgot about him. He's defs a good sensei.