anyone know which one of these drives are holding up the best?

IMO no the scx lowers are massive and scrub speed. The new Bmax owner has upgraded propshafts and although it has xr lower gears there treated and have been proven in 800+ hp. From what I gather throwing in a set of lower gears every 2 summers should prevent failures, the bmax already has a stout vertical shaft and offer 3x stronger propshafts that the owner says are withstanding 1500hp!
But imo the common bravo failures are:
1. Vertical shafts
2. Prop shafts
3. Upper gears or housing flex
4. Lower gears

really depends on what boat, weight and hp if you ask me, my 42 fountain ran bmaxs with blown557s and i ran it hard and broke 1 propshaft in three years, gears were ok,