They are all good as each one can be for a different expression but for a normal look the first eyes are better as the are about normal size for that pallet size.

perhaps you should avoid  that AA you're doing. for such an small sprite, you need each feature well defined instead of blend it all together.

about the eyes... they are quite unreadable, at least on my monitor. the only one i could identify as that without zooming in was the third one. but i must be honest, i though it was a face line this n_n

now... i find it weird that, due the lack of features, you can easily flip these faces upside down and acheve the same result. = not sure how good that could be.