There are many opinions on which regulator one should get.....that's why there are so many different regulators out there.
First, what kind of diving do you plan to do? What kind of diving do you see yourself do in the future?
15-20m dives max looking at neat fishes in warm waters? Then truth is that pretty much any which regulator you can get your hands on will work for you and deliver all the air you should need. Or do you see yourself eventually doing deep dives, 50-60m and beyond, under strenous conditions? In that case, you may want to get the "best you can", i.e. overcompensated, environmentally sealed and all that.
Secondly, what's your idea of "taking care of your regulator"? If it's tossing it in the bathtub when you come home after a week of diving, then keeping it around in some unspecified condition? In that case, you may want a reg "as cheap as they come" and plan on frequent replacements (and plan on staying relatively shallow). Availability of service and spare parts is then a no-issue, since you'll probably just by another "cheapie" cheaper than paying for service. On the other hand, if you take care of your reg and plan on using it for many years, then getting a "brand" and at least a mid-range type reg. where spares and competent service technicians are available not just "close to home", but everywhere you may think you will go, may be the thing to do.
Me, I personally use AquaLung exclusively. One reason why I picked those over the other good brands since where I live is serviceability: parts are easy to come by, parts which must be factory ordered are ready within a few days. Some of the other brands (e.g. Mares -- which also makes excellent stuff) is more difficult to get serviced: spares may be a long long time underways and are not commonly available in stock locally so every repair is a "wait 3 weeks while we get part XXX"-affair.
Another reason is, that the first AquaLung I got served me well (and continues to service me well), and so I have just kept with what I had a good experience with. What works, works, right? I now dive AquaLung Legend LX Supreme regulators as my primary and backup for back-gas and AquaLung Titan LX for stage/deco bottles. Since I occationally do deep(er) dives, where a regulator defect can be fatal, I like the fact that worst comes to worst, my stage/deco reg's can be used also at depth (and, if need be, fitted to my back-gas)
I've had other regulators, but the above have become those I prefer personally. Just because...
So, with the experiences I've had in mind, if I was to start buying equipment today, I would probably buy an AquaLung Titan LX as my first regulator. It's relatively affordable and can serve for a long time: at first for back-gas as primary reg, then possibly later as backup and/or stage/deco reg etc.
However I am sure that similar stories can be told for Mares-brand regulators -- or any other brand, for that matter. The above is just the path I'd taken and that I'd take again.
All of the regulators mentioned here so far are excellent! I didn't see Atomic regulators mentioned and I happen to think they are great regulators as well.
