From my experience here in CO, a lot of the condensation issues arise from a lack of air movement. We have a beefy 4-season tent that has great ventilation, but if there is no air movement, we almost always end up with condensation on the inside. I'm not so much worried about this when it's nice out, but if we're up at berthoud pass and it's blowing snow, cracking a window or two to ensure we get some air exchange won't be comfortable.
The fantastic fan is built in such a way that even cracking it a little in heavy snow could result in snow getting in the van. And, the lowest speed on the fan is going to be too much airflow in the winter.
The maxxfan, however, has 10-speeds and because of the way the hood is designed, you can open it at anytime without too much concern of anything getting inside. You can also have it open when driving or raining. It's a bigger footprint on the roof, but seems to occupy the same vertical space when closed and open compared to the fantastic fan. According to this review, the maxxfan on speed 1 pulls 0.1 amps compared to 1.0 amps from the fantastic fan. Given the range of speeds and CFMs on the fantastic fan, I think speed 1 on the maxxfan might be slow enough for winter use.
At least from a design point of view, I really like the way the maxxfan's hood raises up and down, but the intake/exhaust is always pointed down. From what I've read, if the rain sensor on the fantastic fan closes the lid, it doesn't re-open it. I would feel comfortable leaving the maxxfan cracked open and on speed 1 24 hours a day while we're away from the van.
Fantastic Fan vs MaxxFan Comparison, including amp usage - Truck Campers - Wander the West