Hi,
From your original question, having used all of these regs, I would say by far, the best breathe is the Mares Abyss.
However, by a long shot the Apeks regs mentinoed are the best value for money and a very, very good breathe. They are also possibly the best all-round reg, because they are more furture-proof than the Abyss. They are more streamlined on a twinset, should you decide to go that way, which means you don't have to buy more regs in the future.
You can get a good streamlining from the Posiedon, but they are more expensive to service and I think the breathe on the Cyclone is actually more superior than the jetstream - but that is a personal preference.
Good luck with the decision.
Jeannette