I've owned the S600, G250V and A700 paired with both the MK 25 and MK17 (in that order), and I can assure you that you're going to experience mouth fatigue with any/all of them.....because you won't be able to wipe the grin off your face. Lets face it, there's a lot of great gear available these days.....especially if you're a warm (45+ degrees), shallow (<130') water diver...and in that circumstance you'll be delighted with any of these systems regardless of whether you choose based on price (G250V, MK17), size/weight (S600), or bling (A700). But things change significantly if you're planning on doing really cold water diving (i.e. if your temp starts with a 3 or 4), especially if it's cold, fresh-water. When I purchased my MK25/S600 I was reassured by many on-line reviews, a Canadian Scubapro dive shop, and even a fair number of posts on this forum, that this was a premium system for all water temperatures/conditions. Based on this information, my buddy and I bought identical systems and we each experienced two free-flows on our first dive weekend below 45 degrees (two shallow, two deep, two at about 41 degrees, one at 39 degrees, one at 37 degrees). Next came the MK17/G250V....better, but still one free-flow. Then ScubaPro unveiled the A700. IMHO, when paired with the MK17, you'll have a difficult time finding a better performing system anywhere. Especially if you're doing cold water diving, and/or diving with a lot of suspended particulate. The metal body of the A700 provides much better thermal mass and conductivity to avoid freeze-ups, as does the sealed MK17. I have found it to have outstanding performance in any body position, at any tank pressure, at any depth (only up to 130' tested personally), in any water temperature (only 35-85 degrees tested personally), and in fresh or salt water....and NO Freeze-Ups/Free-Flows in 150+ dives. My son (now 13) and I have used this pairing for the past 2.5 years and even though it's heavier, neither of us have experience any jaw fatigue with it. When you watch your air erupting from your frozen reg at 100', the couple hundred bucks you saved seems much less significant. My personal philosophy is that there's a lot of ways to save a couple hundred bucks (Bar tab, Wal-Mart, Cable, Staying Married)....none of which should include anything that your life depends on. But I digress.....
(BTW I'm in no way linked/sponsored by ScubaPro....but I'm open to offers
!!)