On the issue of which brand, in terms of availability:
Zeagle, Atomic, Cressi Sub (and to a lesser extent Oceanic) are not as widespread. Hog/Edge is utterly nonexistent in island shops, but when they sell parts direct that is not as big a factor if you want to invest in your own tools. But spending the money on the tools to service them is a personal choice, and a many factored one.
On the issue of which brand, on the basis of longevity:
I love Atomic (the titanium ones only) second stage regs because they are resistant to death by corrosion (which kills all other seconds stages eventually) and they are resistant to seat wear by being left unused. Every other second stage accumulates wear when it is not being used (well except for really old Sherwood, but those really suck anyway). Atomic does not suffer this wear because it has the 'seat saver' in the second stage.
On the other hand, in first stages, Apeks was the first one to be essentially corrosion proof with their dry environmental seal At one time that put them way ahead of any other first stage. But when Aqualung bought them and incorporated the dry environmental seal into their line of first stages, and Zeagle and Oceanic went ahead and just started making their own versions (regardless of patent status) that spread to most manufacturers. Now Oceanic (with the DVT) and Aqualung (with ACD) have closed off the final bad corrosion area with the inlet protection system, they have leap frogged to the head of the pack in first stage design.
ScubaPro makes good gear certainly but the open piston design means that most of their first stages will fail from corrosion eventually, and their (non titanium) second stages will eventually fail from corrosion as well. I personally have killed several MK15s amd several g250s, and the amusing ways in which their older regs failed from corrosion put me off chromed brass for good. Great regs, great breathers, maybe not so long lasting in extreme conditions. This was always the strength of the old US Divers regs because being non balanced, the pivot points which suffer the most corrosion were all on parts replaced at the time of service. The SP went for an easier breathing reg, that used a fixed, non-replaceable pivot point which could doom the air barrel to death by corrosion.
Now the corrosion race (or the race against corrosion) goes to USD (US Divers/Aqualung) or Oceanic's dry environmentally sealed and DVT/ACD first stages. Atomic's Titanium second stages(not their Zirconium second stages, which corrode worse than chromed brass, and not their stainless steel which is resistant but not immune to corrosion) are the clear winners in the second stage battle against corrosion. Other brand's titanium second stages may last as well, but it seems like alomst every one else mixes some titanium parts with other metals parts like a stainless lever, and just call it Titanium. Atomic's second stages are all titanium, at least all the metal parts are. Some of the plastic parts of Atomic second stages, however, are apparently made of compressed sawdust though, because they fail with U/V exposure pretty quickly. It almost seems like (some of) the plastic parts in Atomic second stages are built to fail, because the titanium parts never will.
Get new Oceanic or USD dry environmentally sealed reg because their new first stages are setting the pace. The second stages will eventually fail from corrosion, but the first stage should be good forever with the DVT/ACD feature and the dry environmental seal. If you want a lifetime second stage consider Atomic but be aware that you will need soft parts at some point so having a dealer nearby helps. Although the internet is changing that, Atomic does not technically allow web sales, or at least hinders them greatly, and their dealer coverage is not the best, so a move to a new location may leave you without a nearby Atomic dealer. On the other hand, Atomic (unique among ALL manufacturers) lets you send gear to them for service, and they apparently replace all the plastic bits for free when they overhaul the regs they are sent.
Get the LDS tech to tune that bad boy super-fine and you'll have a lazy breathing reg for under $400 bucks. 
