To me, Aurier and Trippier is a toss-up.
Both of them are neither great or bad. Both are just decent.
I’m on the fence too with Trippier. Granted he doesn’t have nearly the pace as Aurier, and has somewhat less defending skills, but he does bring something extra in the attack. One touch passing and crosses are excellent.
Aurier is is more agressive defensively, but to a point he has some pretty wild tackles.
Serge would definitely be my first choice, but I wouldn’t sell Trippier.