To the best of my knowledge, Uniswap is a decentralized exchange (DEX) and with the rate it is growing, I think I have every reason to believe it is becoming the best Decentralized exchange. Also, to remain at the top comes with many things and one of the most important is consistency, that is, if the team can be consistent and true to their goals and objectives, then Uniswap can be regarded as the best DEX. Currently, I can't think of any Dex that can challenge Uniswap both in terms of liquidity, users and hype; just like it is in the case of Binance wherein people clamour for new projects to list on Binance, same is going for Uniswap wherein people now clamours for new projects to list on Uniswap.
To answer your question, I would say it a combination of both hype, liquidity and seriousness of the team. Binance didn't rose to such height by sitting down, the team did many things and took many steps, so if Uniswap can do that as well, then it can be the best and maybe most powerful DEX.