We have carried Rheem for years and it has been excellent with little problems. I firmly beleive that most equipment problems are due to installation or other service problems, such as parts changers. Some brands sell to anyune and their reputation suffers because of it. But they sell the most, depends on your goals I guess.
I always did 2 brands under the theory that if you couldn't afford the best then you were looking for cheap. Boilers were Buderus and Utica. Air conditioners were Ducane and American Standard. Furnaces were Thermo Pride and Hallmark.
I rarely ever did a furnace and instead I converted nearly everyone to Hydro air using first company air handlers. Loved those jobs!.
Oil Heat only
The shop I work for is a Carrier FA dealer. We occasionally install Day and Night (cheap Carrier) or very occasionally Goodman for a cheap job. Boilers are generally Burnham/New Yorker or Williamson for the real cheapasses.
Commercial rooftop jobs are the same. Carrier/Day and Night/Goodman.