It depends, honestly. If you have a pet with auto hp, the drain aura isn't quite as useful. I suppose the answer is the dark aura, until you can hit damage cap, then the blue aura would be the next best thing. If you're in a party with two Battle Mages, I would probably have either the Dark/Debuff or Dark/Drain on.
Pretty much, the Yellow Aura is nice, but probably the least useful.
I found Hasty Aura the most useless to me since my attack speed is as fast as I need it to be.
I only use Dark Aura for bosses that have some serious defense, or have waaay too much hp than they really outta have. *Glares at Hilla*
Blue Aura is surprisingly useless for me because of Drain aura. The added resistance when active isn't really a whole lot than what the passive already added. Yes. Every added point counts, but as it is I can ignore most effects bosses try to slap on me without it.
I'm really loving this Drain Aura A lot! Especially since I'm recovering mp as I attack periodically, so I'm "almost" invincible! Although random DRs or OHKOs catch me off guard off times.
I'm still trying to figure out how Weakening Aura works, so I have no real opinion on it... yet.
Also on a funny note, before the update my Magic defense was (obviously) better than my weapon defense. (Although when I had Adv. Blue Aura active both maxed at cap.) Now my weapon defense is better than my Magic!(?) Seriously that's really weird.
I prefer Blue for aesthetic purposes (also stat resist is nice)
I use Hasty for training, Dark for bossing, Drain is useless for me (but I haven't gollux's yet, might be useful there), and Debuff I kind of just afk and it works, not sure of its ramificarions on damage.
As @Carbyken: has stated, quite a bit of mdef was lost (like 13k mdef, while wdef remained intact)
@Fryber: Actually my weapon defense grew more higher than what it was previously. I can't remember the exact number, but I believe it was around 7500-7900? Now it's 9734! While my once capped magic defense drops to 6741!(?) (With the added Hyper magic defense of course.) Also when I added points to the Hyper Defenses, Weapon defense was about 7--- or so, and jumps to the current number previously stated. However magic only grew to the usual +500 like it should. Now I'm not complaining entirely mind you, but some consistency is all I'm asking really.
@Carbyken: Mind you, I'm not complaining about this either, I just find it rather odd that suddenly 13k magic defense could just vanish into cyberspace. (22k->9k as I mentioned earlier; however, my wdef was almost 13k and is like 12.7k now) I wonder if we'll ever find out the source of the missing mdef.