Eggshell or even better, satin. Some go as far as using semi-gloss.

No painted wall stands up to a damp towel....for long.

Choose a bath paint or at least a satin sheen. Keep moist towels away from painted walls.

Michael

I used SW Duration matte in my master bath and it looks like eggshell or satin to me (definitely has a light sheen-very attractive finish) and DH and I are very careful about cleaning up after ourselves.. But in a bath used by a lot of critters, maybe you'd want the eggshell or satin.