I think Ethereum's biggest competitors are Binance and EOS. Even though Binance is not a smart contract platform, BInance has tremendous community strength, BNB marketcap might be able to overtake Ethereum later.
Binance and EOS may be superior than Ethereum in terms of scalability, but they're utterly centralized. In this sense, BNB and EOS cannot compete with Ethereum directly. It's like comparing apples vs oranges. Decentralization will ultimately prevail in the long run, since it's what makes Blockchain technology good. Despite the high fees (sometimes) and slow transaction throughput, Ethereum has been the #1 choice for dApps and tokens due to its inherently-decentralized design.
If we were to compare different smart contract platforms based on their decentralization, Cardano would prove to be a real contender against Ethereum. Whereas other alternatives rely on DPoS and other BFT algorithms for consensus, Cardano will be using pure PoS from the ground up. This allows it to obtain a greater level of decentralization than its competitors. With this in mind, Cardano might be able to become as good as Ethereum someday. If the team develops the platform as promised, ADA will become the second-most decentralized cryptocurrency after Ethereum in the smart contract space. The slow and steady development phase of the Cardano project allows it to be more stable than TRON or even EOS. Binance Chain, on the other hand, is currently more centralized than the aforementioned platforms, being completely out of question.
In the end, people will continue to use Ethereum because of its strong ecosystem of developers, dApps, and tokens. But there's room for growth for other competitors as they bring new and exciting features to the smart contract space. Ultimately, there will be only one winner, and that's Ethereum. Cardano will be taking "second place" in popularity and mainstream adoption, followed by TRON, EOS, and lastly, Binance Chain. Just my opinion