Like with dive computers, the best brand is the one you own. I have a Atomics B1/T1, so of course it is the best! Seriously, though, there are lots of good regs out there from many manufacturers.
My B1/T1 has very low work of breathing, really smooth. Reasonably dry in all attitudes -- breathed dry even when out of boredom I decided to do a safety upside down vertically.
Although it has a 2 year service interval, twice now I've had it serviced around 12 months, 100 dives/ 80 hours due to minor IP creep.
Z1 is less expensive alternative and all you really lose is the LP swivel and the 2 year service interval. M1 is a newer model that might have some improvements over B1/T1, but I don't know for sure.
Charlie