You are correct! All of the other bases have a full positive charge on the atom adjacent to the oxygen atom that has the negative charge. This will attract the electrons on the charged oxygen atom and make them less available for sharing. Another way to remember this is that the acetate ion will be the strongest base because acetic acid is the weakest acid in the group. A strong acid must logically create a weak conjugate base or the acid could not give up the proton readily.