I say that both fw and sw are even for best fish. Some people would argue that sw has more colorful fish but some african cichlids are just as colorful as sw fish. Also fw has better predators that could be kept in tanks. But then again sw has sharks, rays, octopus etc.
For home aquariums Id go for FW. But since the question was pretty general, I voted SW.
There are alot more SW fish out there and most of which Im sure havnt even been discovered yet. Watching those deep sea documentaries always leave me in awe.