Beside Uniswap and pancakeswap exchanges popularity, Idex is still one of the best Dex exchange before the launch of the Uniswap and pancakeswap. I think polkadex, Biswap, 1inch exchanges are still popular among many other exchanges out there
in additions, the popularity of some these Dex exchange depend largely on the earlier launched, the marketing/promotion of the exchange plus the cost of trading transactions.