Which are the best competitors to Ethereum, and why do you think so?
(I know on top of my head that Cardano and IOTA try to challenge Ethereum,
although they still haven't proved much from my understanding?)
Ethereum has competitors. This has been said more than once. One of them is NEO. But whether he can take the place of the main altcoin I do not know. Probably not. Since the air Is more in demand now.