Over, I've always have it over. The only time I've had it under is when my helmet didn't have a strap loop. I saw under the helmet as just another fad coming along, and was uncomfortable for me so I never did it intentionally.
over i think it looks better and not retarded like under the helmet plus im sure if u put ur gogs around usin the strap in the back of the helmet or not it works 1000 x better than under the helmet