between the first and second time HK-47 was owned by Darth Revan, didn't most of HK-47s masters die? usually by his 47s doing? I could see owning HK-47 backfiring horribly.
Same thing with PROXY, his main programming was to kill Starkiller, he could take that as programmed to kill his master, and KaBoom- you are dead
Guri is a dangerous choice as well, one bad move and your head is facing the wrong direction.
I'm going for 2-1B, i keep getting hurt, save a lot of time at the hospital, plus you could rent him out, make him pay for himself