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

learn fresco at http://FrescoSchool.org

fresco painting video tutorials: http://www.FrescoSchool.com

also visit

Fresco School Video Channel
http://youtube.com/FrescoSchool

Contemporary Fresco Gazette
http://trueFresco.Org
commission fresco or mural http://iLAdesigns.com