I use wood for everything on the inside if it is possible.  My main reason is wood seems nautical and has such a nice warm look.  When i bought my boat all the teak trim was left unfinished.  A couple of years ago I brought it all inside and put several coats of Semi-gloss poylurathane on it.  I was surprised to see the teak covering all the little cubby holes on the sides had some mildew growing on the back side.  I think this is just do to the warm humid atmosphere it lives in.  Any way, I but several coats of the polyurathane on both sides thinking it my stop the growth on the back side and if it didn't, it would at least be easier to wipe off.  

Regarding exterior varnishes, I used the Cetol natural color covered with about 4 coats of Cetol gloss.  On the inside, I discovered Miniwax (Home Depoot) sold a SparVarnish made up of Poly, for boats.  I used that on the inside and for $11 bucks a quart I would recommend it for any inside work.  There is so much hype on all the different external finishes, I am a little afraid to try something different considering the amount of work you have to put into it.   LL