Poseidon regulators, since 1977, for the sheer quality; and the fact that I am still able to use and find parts for an even earlier, inherited Cyklon 300 as a bailout -- nearing fifty years of age -- is one of myriad reasons why; that, and the fact that I have used them from freezing to the tropics without ever so much as a hitch, in all of that time. They breathe like a dream if properly maintained.
O'neill wetsuits, for their quality and fit; and, also to support a local business, of my hometown of Santa Cruz.
Scubapro compressed-neoprene drysuits (because I never cared for the garbage bag experience of trilam); and because O'neill no longer makes their Supersuits.
Scubapro; Poseidon; DGX "Jetfins," for my frog legs; like their weight; they suit my swimming style.
Suunto and Poseidon computers, AI and not; Poseidon analogue gauges.
Poseidon / Divex watches, for when, not if, the electronics crap out.
Zeagle BCs, because every part of them is easily replaceable, and held together with grommets.
Cress-Sub masks, to fit my "Eye-talian" nose; Poseidon FFMs, for those cold or nasty waters.
Too much other stuff to mention . . .