I have a list of my favorite smarties:
http://www.comicvine.com/myvine/dhu/smarties/75-6653/

I don't know who is actually smartest, but my favorites are:

Marvel:
Forge
Moira MacTaggert

DC:
Mr. Terrific II
Ted Kord (Blue Beetle)

Other:
Gyro Gearloose
Dr. Benton Quest