Most the brand names are going to be good. Some regulators won't be good if you are going into tech diving, i.e. deeper than 130 feet. Some will breath easier than others. Some will let water in (breath wet) in certain positions. They will all be fine in a face down, horizontal position. Some, like my current regs, will breath wet when you are upside down.
If you are just going to be a recreational scuba diver, most regulators will be fine. The thing you have to watch for is maintenance costs. Worst case is you buy regulators and cannot find anyone to service them.
Some examples, lets say you find Mares and Sherwood regulator set. The shops which services Mares charges $35 per stage (primary, octo and first) and parts are typically $23. Annual service would cost $128. The Sherwood shop charges $45 for the set and parts are typically $7. Annual service would cost $52. If the Mares was on sale for $399 and the Sherwood was regular price at $449, it might look like the Mares are cheaper but after your first year of getting them services the Mares would cost $399+$128 ($527) and the Sherwood would cost $449+$52 ($501). Every subsequent year, the Sherwood would save you more and more.
These are fictional amounts. It could be in reality the Mares are better priced then Sherwood. The point is, initial purchase price is just part of the cost. Maintenance tends to cost you more because you will, hopefully, be servicing them for years and years.