Apeks DS4 and DST first stages, with TX and ATX 40 and 50 second stages. My primary buddy and I already had Apeks regs in common when we started collecting regulators so we stuck with them. We have come to appreciate having only one brand, and models that share nearly all common parts. It makes keeping them in repair much easier, if you're DIY.
With an increased number of regulators comes the increased chance that one may not be functioning correctly. It can save a dive if you're able to swap them into any role in your system. So, we don't down grade our deco or O2 regs. DS4's are rock solid, can be used at any depth that we'll ever see, and don't cost a mint. The DST's made their way into our program because they were available second hand at very reasonable cost. The swivel makes it ever so slightly easy to route deco/stage hoses but can pose an additional o-ring failure point. How significant is this? For years I've never thought twice about it. Until, this summer when we had a turret bolt somehow work loose enough to allow the o-ring to extrude during predive checks. It subsequently leaked do to the damge it suffered, and required an otherwise already overdue servicing. But, then again, all the swivel equiped regs(atomic, SP, DR) share this potential failure point.
