I say we shorten Aqua Ring to 5 actions but make it heal 4 HP per action, and make it 12 Energy. My reasoning:
5 actions * 4 HP per action = 20 HP recovered over 5 actions. Essentially, this means 1.6 HP recovery per Energy.
Leech Seed, meanwhile, heals 18 HP for 10 Energy, which is 1.8 EN per HP; however, it also damages the foe. Although in most cases this makes it seem like it is superior to Aqua Ring, remember that the 4 HP/action recovers HP faster than the 3 per action from Leech Seed.
Essentially, this means if you have a Smeargle or something, you can either pick damage or faster healing, as there is no Energy difference and only a 2 HP difference.
Meanwhile, there are flaws with other options (albeit, their are flaws with my idea, but nonetheless): Unitas' Water immune perk makes Aqua Ring rather underpowered. Meanwhile, the 12 action duration still highlights Aqua Ring's largest flaw: Aqua Ring, as it is currently, only heals 2 HP per action, which is very little in a fast-paced game like ASB. Sure, it's nice for nullifying Burn or Poison or whatever damage, but there is the notable flaw that 6 HP per round (4 in Triples+) won't save you, unless you're trying to Endure your way to victory, in which case you probably don't have the turns to set up Aqua Ring anyway. Infinite, meanwhile, puts a large emphasis on stalling out turns, and it turns into a Protect and Dodge war. On a similar note, doubling HP recovered, though it may seem like it fixes the aforementioned "largest flaw" of Aqua Ring, has the disadvantage of being able to recover 24 HP in 6 turns; though it could be argued moves like Roost and Recover heal around the same thing in 1 turn, remember that Aqua Ring does not use up a recovery move, and, likewise, can be used infinitely, allowing the user to essentially stall out the 6 turns indefinitely if they repeat a good pattern (and possibly get lucky with Dodges, but that's a whole other discussion). Meanwhile, if Aqua Ring is modified so it does take up a Recovery move, then I could see doubling the gained HP feasible; in fact, I'd say that 3 HP per action for 10 actions but taking up a recovery move would be a nice improvement, as 30 HP in 10 actions is good enough to count as a recovery move to me.
tl;dr Aqua Ring should heal 4 HP per action for 5 actions but have its Energy increased to 12, or make it heal 3 HP per action for 10 actions but take up a recovery move.
Feel free to shoot my opinion down, I guess.