so your first concern would be - cleaning and graffiti removal.

then the color stability, then the medium life expectancy.

aside from true fresco, the longest living medium would be acrylic.

lime wash you cant quite clean.

also walls fail first, so make sure you do not pain directly on the wall... make it removable...

80% all those are removable (painted in the studio and later installed):

http://frescoSchool.org/kent_twitchell

also visit
Contemporary Fresco Gasette http://trueFresco.Org
___________________________
learn fresco at http://FrescoSchool.com
commission fresco or mural http://iLAdesigns.com
showcase your art http://truefresco.net/gallery
Art Search & Art Directory http://truefresco.org/link_directory add your site