ethereum is a good altcoins but i don't see them transparent in development, even the rumored eth 2.0 will launch, not even launch as of today. In my opinion, the criteria as a good altcoin are having a large community, high security and adoption.
actually there's a lof of altcoins with large community in the space but sad to say despite, most of them are still not worth it because they always end up very stagnant after all. So if we were talking about long term then for me no other than ethereum..