Various positive factors, but the one I personally like best is that the 5320 is a rare Patek perpetual with a seconds hand. Also I prefer the more refined pushers of the 5070 and 5170 rather than the less sophisticated pushers of the 5172.
I also remind myself that nobody cares what watch I’m wearing. It’s a very personal thing that only I care about and that makes me happy when I’m wearing a certain piece. I tend to let things happen organically rather than going by some particular criteria or organized plan.