Forewarning: I'm just beginning testing on this. Since everyone on the guide thread appears to be more concerned with RMEA and Weapon skill Sets at this point, I'm putting my focus and attention on my utility sets while I slowly whittle away at my Apocalypse on the side. This will take some time so I will be updating as I go along.
OK! Now that I've gotten that out of the way...
I don't know about anyone else but this has been bugging me for a while whether Dark Affinity+ will genuinely overtake Drain Potency+ gear over all. The easiest slots I can test this out on are Head and Body comparing a Pixie Hairpin+1 Vs. a NQ Lugra Cloak. (I'm using NQ since it's a flat +30% and I want to compare with a flat round number)
Side Note: Since I don't actually own one, I'm borrowing a Hairpin from friend(s).
Starting with small sample size:
10 Drain III casts on Lv.0 Rabbits in West Ronfaure Naked.
HP: 1749 / Dark Magic Skill 456
791
819
841 Highest (So Far)
744
673
756
696
811
655 Lowest (So Far)
803
Average: 758.9 HP Drained.