Lol that's a loaded question. Guess during the week would be your best bet. We always liked milledge as it was furthest away from all the action but it's also the longest trail ride in.
If your looking for least amount of traffic id suggest riding belle in McBride, in Vale I typically find Chappell has the least amount of sledders as it is the further from town and longest trail. Allen is by far the busiest on any given day. Although it is the biggest area and the best on a sunny day as you can push back for bowl after bowl to find fresh, great tree riding in both areas
Belle is real small.... good for an afternoon ride. Best bet is get to know some of the areas and continue exploring them. You have plenty of options in Vale. Alle, clemina, chappel, Westridge, Oasis, Keyhole...... Some of these are best left alone if your new to the mountain scene. Mcbride has lots of riding as well. And if you wanna drive an hour further from vale you get into Blue which has a **** ton of riding.