First, make sure any goggle system you buy actually fits your face properly. A good fit is essential to the goggle working properly.
Second, take a look at the goggles that offer thermal lenses. a thermal lens will decrease chance of fogging, and when coupled with a fan, could eliminate it completely.
Third, change your lenses out regularly. When i was playing regularly, I was putting a new lens in every 3-4 months. This not only helps keep the fogging down, but ensure lens integrity.
The Tier One Tactical Operator
Tippmann Arms M4A1
KWA USP .45, KJW P226, KJW hi-cappa