I kinda see Ethereum killers in groups.


SoLunAvax

Solana is the cheapest
Luna is the most decentralized and allows you to choose what you use as gas (love this one)
Avax is in between and generally more serious than Solana


Mathematical ones
Cardano (first mover advantage, but programming language too hard for normal people)
Algorand

Upcoming Killers
Harmony (quite decentralized, great theme, don't know enough about it yet)
Fantom (don't know shit about this one yet but it's more decentralized than Sol and Avax)
Probably many others

I think one of these mentioned is going to overtake Ethereum one day, although I'm not certain as a newer one might be better than all. Personally I like Luna the most, for using, but its community isn't that good yet, and its already so high. I'd stay away from Solana especially.