My view of what defines a "good regulator" has changed over the years... a while back I got my DM cert and started working with an LDS (specifically with their repair guy...)... I had a opportunity to see the guts of a number of different regs and listen to him give his impressions on what made a good reg and what didn't...
Personal Choices: Now... I dive Aqua-Lung Legends... great regs... love em'... have a Sherwood Blizzard on order for my ice diving pony... also just had the Legend first stage "retrofit" by the LDS to make it an Aqual Lung "Glacia"... I've also dove a variety of other manuf. ... They all pretty much 'work'... and I really haven't found a regulator that... from a a pure functionality point of view I WOULDN'T dive with...
Decision Points So... where are *my* decision points? First I've discovered the joy of "simpiler is better"... have your Aqua-Lung reg overhauled and look at the pile of parts you get back (if you get your parts back)... now... have a Sherwood overhauled and compare the pile size... (Fewer gadgets in the Sherwood... )... As our tech points out (... and I tend to agree)... simpler has its merits. (He really doesn't like regs with 'swivels'...
) "The more parts and gadgets you have the more things can break"... quote from da' repair guy...
... and, as Papa Steve pointed out... being able to have your regs serviced is, in my opinion... one of those critical decision points...
Recommendations Whatever reg you're looking at... talk to a repair tech and find out how much an overhaul kit costs... a lot (most???) reg manuf. give free parts... assuming you have sent in the warrantee card... don't miss an annual servicing... etc... Great program... but if you DO miss... (happened to me...)... how much are you going to pay for parts when you do haul your rig in???
There's a lot more to *cost* than the initial purchase price...
Do you see doing any COLD water... or Ice Diving in your future? Spending enough to get something designed for this kind of diving now can save you having to have your gear retrofit... or buying new gear in the future (... all part of the cost picture)...
Now... I won't get into "buy LDS" or "buy on-line"... that's a decision each must make for themselves...
Final Perspective Always remember... no matter WHAT you buy... they'll make something better, niftier, shinier and probably on sale with in 30 days (or there about) after you buy whatever it is you end up buying... and you'd better like whatever you buy because you and you're reg are going to develop a very close and personal relationship...