Look for liquidity and most importantly all statistics & analysis. If you don't understand what I mean, you can check uniswap info by searching it on google. You'll see uniswap has their own statistics.
Factors to consider when choosing a DEX:
1. Daily trading volume: The higher, the better, as this indicates that the DEX has a large user base.
2. TVL and LP: The higher, the better, as this helps to reduce slippage.
3. Trading pairs or number of tokens listed: The more, the better, as this gives users more options.
4. Order options: The more convenient, the better.
5. Uptime: The longer, the better.
6. Team: The more reputable, the better.
7. Tokenomics of the native token: This affects the future of the DEX.
8. Legal status.