The Automated Market Maker trading institution (AMM) is a cornerstone of decentralized finance. This study directly compares price efficiency and liquidity between the continuous double auction (CDA) and the AMM in a controlled laboratory setting. Employing a clearly defined asset with known fundamentals, we find that the AMM significantly improves market liquidity with markedly higher trading volume than the CDA owed to the convenience of not having to wait for a counterparty. The degree of mispricing in AMM is comparable to CDA but with much smaller volatility. Experience has similar effects of reducing mispricing in both trading institutions, though the properties of high turnover and low volatility prevailed even with experienced traders.