Stellar DEX: specifically for Stellar-based coins and it is very difficult for beginners to learn, unlike Ethereum.
Waves DEX: It's pretty crowded if we see a comparison between the Stellar DEX market which is quite difficult to learn.
In my opinion, I would choose Waves DEX for my trade because Waves DEX works almost the same way as Ethereum DEX, such as: ForkDelta, IDEX and EtherDelta.