@PretzleMe
It isn't that I think Sloane will never backstab me, it is the way and method of their doing it when or if it finally happens.
Sloane...
Will take a hit out on you, probably with Outcast attack group, after throwing you out of Kadara port. You will also probably get some kind of notice or warning by her change in actions, and then the bullets will fly. If you are good, smart and lucky, you will kill her assassins, and take her out, all pretty much above board and straight forward.
Reyes...
First you will know, is your allies are backing away, your reputation is in shreds and you have few friends left.....then either another enemy will come at you with inside info on you or Reyes will set you up in a trap for you to die. If you survive, you will have a bunch of work to repair all the damage he did, BEFORE you realized he was tired of being your ally.
So of the two, I would rather deal with Sloane, while neither is straight up trustworthy, I feel Sloane is more straight forward and thus better as a frenemy....Plus while she doesn't respect the Initiative nor Ryder in the beginning, after everything, she does respect Ryder and is a close to calling him/her a friend as Sloane will ever be while she is in her position. Doesn't mean she still wouldn't attack Ryder if she felt the need, but there is Respect.