Better at what? Both have confidential txs. Monero adds one time stealth addresses and ring signatures in addition to obscure the transaction graph (Liquid doesn't). Monero wins that hands down and soon to have full chain membership proofs to completely hide it. I don't think Liquid even has plans to improve privacy afaik. Liquid daily transactions are significantly less so it's anonymity set is much smaller. Liquid has no p2p market presence. Not really used anywhere. Both have low fees. Liquid requires permission from a federation to peg out. All Liquid really has going is it's value peg to Bitcoin if you held for the long term (several years). But if I'm only holding and not using why not just hold actual Bitcoin? Short to medium term performance of Monero vs Bitcoin has been a toss up.