I would go with a bristle nose pleco or sailfin pleco aka gibbacipe. Both will clean the heck out of a tank and they are affordable. The sailfin do get a little larger than 12" tho. Both of the plecos I mention you can get in albino some people prefer albino cause it easy on the eyed.
GOLD NUGGET and PHANTOM, mainly fancy pleco DO NOT CLEAN they just look cool.