I started airsoft with what I thought was one of the "best" low/no fog full seal goggle options (ESS Advancer V12). I bought defog spray, and pre-treated them too. Worked mostly very good, but they still fog/condense in the heat, especially when you stop moving around for any extended period.
Switched over to Smith OTW fan goggles and am super pleased. Comfortable, extremely quiet fan, and they haven't fogged at all, not even a little. RX insert for the OTW is $25.
http://www.safetyglassesusa.com/smit...w-goggles.html