Know the difference between Piston and diaphragm regs. With the exception of sherwood piston regulators can not have a true environmental seal without packing it with cristolube, wich is pricey and a headach for tecnicians. Diaphragm regs with an environmental seal would be your bet bet. If you are dead set on scuba pro I'd go mk17 over mk25, but there are les expensive alternatives that perform just as well. As mentioned Hog and edge are good regs and the best bang for your buck. Hollis, Oceanic, Aeris, Zeagle, Dive Rite, Mares, and Aqua Lung, all have environmentaly sealed diaphragm regs and all have free parts kits for life through authorized dealers. So do your research and don't simply listen to someone telling you whats best.