Best bet is to vent it out of the soffit. You'll want to bury the vent hose in plenty of insulation, like 24" of insulation.

My mom has hers vented out a soffit, but it wasn't properly insulated. During the winter you could see a line in the snow on roof where the vent was run. This melted snow caused ice damming, leading to more problems. The duct was insulated, it was under about 12" of blown cellulose insulation, still wasn't enough. I put 2 layers of R20 on top of the vent, no more issues.