I may be unusual here, but my favorite time of year to travel is the winter. If there is snow, that looks better than any other type of scenery in my opinion. If not, the leaves are bare so more scenery is visible. Also, if I'm on a longer trip I can actually appreciate the lack of daylight. The next day is much less enjoyable if I am tired, but it is difficult to get good sleep in coach. If I want to get six hours, I probably need 9-10 hours of laying down, plus an hour to prepare for sleep and waking up in the morning. Meanwhile, I enjoy watching the scenery so much that I can never convince myself to sleep when it is light out. In the summer, it is often only dark for about 8-9 hours, so I inevitably wake up exhausted. In the winter, there's nothing to see by around 6:00 so I have plenty of time to get sleep.