Every single UY can book any trip at the same time so it has nothing to do with booking. What the best UY does is to provide some free insurance against a last minute cancellation by giving you the most time possible to rebook with the points or to allow you to still bank if the points are bankable. To do that you want a UY that starts just before you're normal time of travel and if that is January then it would be a December UY. (there are no January, May, July or November UY's) February would be the worst because your trip would occur right before the UY and you'd always be well past banking deadlines and also have less than a month to use the points before they expired.
If you never have to cancel the UY won't make a difference. If you ever did have a last minute cancellation it might help you save a year or more worth of points.