Neither.
I'd say either get an experienced, defensively solid RB like Lichensteiner or find someone who is all-around better than Bob.
He's doing great going forward but he's just going to be a liability for the next year or so until he gets a better sense of positioning but that's if he continues getting starting minutes a lot, something he shouldn't get if his form continues. I'll be patient with him and don't lash him too much because it's such a hard position for a CM to adjust to but he's already being exploited against weaker teams now and i wouldn't expect too much of a turn around in that sense of his play. Piqué helps cover those holes better than so many people give him credit for and I think it's no coincidence Bob's form has gone to shit without Piqué guarding his back.
Honestly, I always liked Aurier as a player but his off the field antics won't be tolerated here. That considered, Luis definitely had that question mark coming here and for the most part, he's been fine. Not a stretch to say Aurier couldn't adapt and mature here, especially with a more French contingent here now.