trainer mostly due to loss of daylight, and i get tired of layering a ton of clothes & keeping them all washed. I really don't mind using it as much as others do, in fact, I use it even when the weather is nice. It's nice to be able to listen to music, or watch a movie & ride at the same time. Makes the time go by quickly. That being said, I usually always try to ride outside in the winter on the weekends as long as the roads aren't filled with snow and/or ice. I also ride to work, and will usually take the long way home, even when it's sub zero... but again, as long as the roads aren't filled with snow and/or ice. I do have a hybrid with studded tires though, but won't 'train' with that bike, just commute... and will hop on the trainer when I get home.