I may be biased, but I believe that winter in Moab is the best time to visit. There is way less traffic. There are no lines. It's cooler and may require only a light jacket so during strenuous activities you remain way cooler. The contrast with a dusting of snow on the slick rock only improve the views. There usually aren't fire bans during the winter where they usually are fire bans in Moab all summer.  Plus the winter is much milder than in other areas of Utah.

Moab seems to transition from a booming tourist town to a sleepy rural town in winter. It's definitely a time for the Moabites to go out to play and have the area to themselves. Trails that have hundreds of people on it during the summer may have one or two people on them during the winter.

Winter in Moab has only two downfalls. First, ice or snow on the sandstone can be close to deadly. Please avoid hiking or biking on the sandstone if there is snow or ice cover. Second, a third of the restaurants and businesses shut down meaning you can't get all of your favorite foods or activities year round.