Sherwood and Genesis are in cahoots with one another. Oceanic and Sherwood are not in cahoots with one another, although certain Oceanic and Genesis second stages are virtually identical. Certain Genesis first stages look like Sherwoods on steroids.
Oceanic and Aeris are made by the same company. You can now throw Hollis in there, too. Oceanic and Aeris first stages are quite similar, but some of their second stages differ considerably. Then, some seconds are virtually identical, too.
Since I've been in the service business, I've developed a theory: the various regulator brands get together at night when the store's closed and in-breed. Face it--there are only so many ways to skin a cat so there are bound to be some similarities between different brands.
You can't go wrong with either Scubapro or Oceanic. For my 2 psi's worth, I'd look long and hard at a Zeagle. I dive one and I love it. I have an old Poseidon that I salvaged from my shop's junk bin that I'm gonna rebuild someday, but that day hasn't come yet.