Kinda obvious. The other one "malfunctioned" (red circle on his face) and can feel. Connor is still a Droid functioning as intended (lifeless and serving).
I think my problem was that at least in that trailer Daniel could of just been a guy. There was literary nothing android about anything he did.
Maybe I'm just nitpicking.
Either way I like this protagonist should make for an interesting guy to have a remorseless machine.