according to my extensive research,
vintage Cherry MX Black are the best Cherry,
Gateron make the best modern cherry clones,
Outemu are good, but inferior to Gaterons (less smooth, the sound is worse)
Cherry are about the same level of Outemu, the sound is just so slightly better. They are also more expensive.
apparently cherry quality has gone down, when it comes to type of plastic used and lubricant.
Then there's Mathias switches, which are more or less a clone of Alps. There's only 3 types of switch, the boards are quite expensive, and whenever i watch a review, everyone just says "they are worse than Alps" but nobody compares them to Cherry; it would be my guess that these switches are better than Cherry, but the boards are all about $150.
Unicomp produces clones of the IBM Model M, with the famous buckling spring keys. They have a wonderful feeling when you use them, but are quite loud (Cherry just do not compare) and in the long run they are not really fast or ideal for typists. Boards are reasonably priced at around $90.
Topre makes a type of rubber dome switch that contains a spring for tactility; also, the switch does not make contact to the PCB, but rather uses a electrostatic contact, so they do not bottom out. While you might think that a membrane keyboard is garbage, apparently Topre keyboards are the best thing you can buy in this universe. Topre boards start around $240, although CollerMaster makes a clone called Novatouch, *slightly* cheaper.
There's also non-clones of cherry, such as the Razer switches. The difference is minimal, i have never tried them to see if they are smoother or not. You may get some answers with some googling.
That's more or less it for new switches. You can but second hand switches from eBay, such as Alps, but most will be not quite as good as a new board, because Alps switches (allegedly) age poorly. There's also some more obscure switches, such as Honeywell Hall-effect switches, Space Invaders, etc but this tendds to be exotic stuff from the 80s and early 90s which 1. you are unlikely to get in working order 2. will be unusable unless you invest in adapters and such 3. are in old boards which are big and use weird layouts, so basically it's only the switches i detailed above.
There is a company that makes clones of the IBM Model F switch, which was apparently even better than the mighty model M, and you can have one for the low low price of circa $350 each.
Mind you, it's totally ok to buy a new membrane keyboard for $20, use it for six months, and when the keys start to get stiff, throw it out.
you can get ALL you ever need to know on switches from this guy:
https://www.youtube.com/user/Chyrosran2