IMO, most beautiful, the one that has in the times square church, cant remember it's previous name.
followed closely by the New Amsterdam.
I dont find the Maruquis that bad, it just needs some sprucing up
for me the ugliest are Gershwin and Minskoff, Lion King did brighten up the place a bit with the murals on the sides of the boxes (or where boxes would usually be) but the gershwin looks like some extruded concrete spaceship.
http://www.flickr.com/photos/27199361@N08/ Phantom at the Royal Empire Theatre