We travel in the summer right now because I teach so we went with a June UY.
Having one that falls just before your typical travel offers the most flexibility in terms of what to do with points in case you want to change your travel, need to cancel, and most important, used borrowed points and then need to adjust.
You can bank during the first 8 months of a UY so if you are traveling during that time and cancel or change to a reservation with less points, at least 31 days in advance, current UY points can still be banked.
If there are borrowed points, the closer to the beginning of your UY you are traveling, the longer time period you have to re-book using those points since borrowed points can not be returned and must be used in the UY they were borrowed in to.
If you really have no set time, then UY becomes less important. Its not that you can not travel during the last part of a UY (although, if buying from Disney, there are rules regarding non-
DVC options in terms of having of when those need to be booked if you want to travel in the last 4 months of the UY) its just that you are at a bigger risk in what to do with points in case of a cancellation.
Good luck!