The glossier you go, the more reflective it will be and as a result, the more likely it is that the paint will show any flaws in the wall. Drywall mud seams, transition lines from mud to paper, etc.

Th glossier you go, the more durable the paint in terms of being able to clean it.

Glossier paints will generally perform better than flatter paints in high-moisture environments like bathrooms with showers.

Personal preference, but a semi-gloss is the glossiest that I usually go.

We used BM Aura paint in matte finish in all three bathrooms, and it looks terrific. We used the regular Aura paint (the Bath and Spa version wasn't on the market yet) in our guest bathroom almost 3 1/2 yrs ago, and it's held up great so far.

We used the Bath and Spa Aura paint in our MB and hall bathrooms (3 yrs ago in the MB and 2 1/2 yrs ago in the hall bath), and they are holding up well so far, too. The Bath and Spa paint is supposed to resist humidity even better than the regular Aura. It might only come in matte finish? We used the regular Aura paint in satin finish on the base molding for that reason.

"Better" is subjective and depends on your use and personal aesthetics. High gloss is the most practical choice in areas with water. Most people prefer semi-gloss or even less shiny paint aesthetically, but some people love glossy paint. I recommend going with your preference, with the caveat that matte paint in small steamy bathrooms will probably not look good for long.

Thank you very much for all the responses above, which are very helpful. I just found out that my current paint is Benjamin Moore's Kitchen and Bath acrylic latex satin finish, not the semi-gloss as I mentioned earlier. It has lasted for more than 4 years and still looks pretty good. I won't go with high gloss for bathroom ceiling and wall definitely. For baseboard and door casing, is it better to choose high gloss? Really appreciate your help.

I have Ben Moore Regal Matte throughout the house, including the bathroom. DS loves steamy showers and I have not had a problem since we moved in Sept 2007. It is perhaps a little harder to clean toothpaste off the walls than a glossier finish, but as someone said, it hides imperfections better. I have found that it isn't so great behind the range with greasy or tomato or jam splatters (I can a lot).

If you like your current paint and find that it wears well in a steamy/messy place like a kitchen, or you don't expect to have to clean the bathroom walls much (no kids or a DH with an electric toothbrush splattering toothpaste) then I say go for the same paint gloss level in the bathroom.

Definitely go flat for the ceiling, but add a mildewcide to the ceiling *and* the wall paint.

I use satin or semi-gloss for trim and eggshell or matte for walls.
Renee