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?)
I think that only those projects that are at the same level with Ethereum can be considered as competitors. There are no such blockchains at the moment. There are a large number of potential competitors, but none of them have come close to Ethereum very closely. At the moment I see a lot of marketing, but not much work. Maybe next year the situation will change, but not now.