I would like it to be a very standard and hackable android phone.
My choice so far is a samsung galaxy S4 mini. I like a smaller phone and I like the fact that it has GSM radios in it that I can use with a third party SIM. I also really need a SD card slot, and the S4 mini has one.
I'm pretty sure this is a good choice, but I wonder if there's another phone I should consider ... I just want something very standard and hackable that I can root with safe utilities (not closed source utilities that might be spyware) and run any android build I want on it ...