The proton on the right is more acidic.
Work Step by Step
In both cases, the charge will be spread between a oxygen, so ressonance isn't the difference. Since there are more carbons next to the oxygen on the left, and alkyl groups act by giving electrons, the stability of the charge on this oxygen will be affected. Therefore, the negative oxygen on the right is more stable, so, the proton on the right is more acidic.