You mention that you could go during spring break, summer, or winter break, by which I assume you mean late December/earlyJanuary. If those are the three times you will likely go over the years then March is possibly OK but December would actually be the best use year. Here, by example, is the use year issue which is really a risk of cancellation issue:
Let's assume a March use year and you intend a trip in March 2016 at home resort. You go online to reserve in April 2015, 11 months out. Because the trip is in March 2016, the "current" use year points for that trip will be those from the use year that begins March 1, 2016. If you have points leftover from March 2015 use year, you can bank them into the 2016 use year for that trip. Moreover, you could borrow March 2017 points for that trip. You can do those things when you reserve in April 2015 because the date you go on-line to reserve is irrelevant to which points are being used; all that counts for that issue is when you will be at WDW.
Now assume you in fact did bank some points for that trip and also borrowed some from 2017 so that your reservation has in it banked March 2015 points, current year March 2016 points, and borrowed March 2017 points. Next assume that in January 2016, two months before your trip, something awful happens, like you get named principal and told you need to stick around during spring break for meetings, resulting in your having to cancel that trip. You cancel and points go back into your account as they are, banked points remain banked, current points remain current, and borrowed points remain borrowed. The banked and borrowed points remain in the March 2016 use year but you will have until February 28, 2017 to use them for a trip. Moreover, your March 2016 points can still be used for a 2016 trip or, by October 31, 2016, you can bank them into the March 2017 use year. The effect of the cancellation is not bad because you still have a long time to do a trip with those points.
Now assume that instead of a March use year, you have an April use year and you set up that March 2016 trip, which is in your April 2015 use year, by making the reservation in April 2015. At the time, you use some points previously banked from your April 2014 use year into the April 2015 use year. You also use your "current" April 2015 use year points for that trip and borrow points from April 2016. Come Jan 2016 when you have to cancel, you have the worst of all worlds. The banked 2014 points cannot be banked again, the borrowed April 2016 points also remain in the April 2015 use year, and your current use year points cannot be banked into the April 2016 use year because the latest you can bank points is by the end of the eighth month of your use year (by the end of November 2015 for an April 2015 use year). Moreover, since your 2015 use year ends March 31, 2016, you will have less than three months to use all those points or lose them.
Thus, the best use year is one that begins shortly before you usually take a usual trip and the worst is one that ends just after the time of your usual trip. Of course if you go at different times of year, your ability to hedge the cancellation issue by choice of use year is diminished. Following the example, March would be the best use year for March or April trips. It is OK for "summer" trips because with cancellation you will still be able to bank curent points and have some time to use banked or borrowed points. But for late Dec/early Jan trips, it is not good because a late cancellation, such as cancelling in early November, could leave you with only a little more than three months to use all those points.
December use year creates a hedge for all three time you could go. December would be fine for March and April trips, because following a cancellation you would still have a substantial period of time to use the the banked and borrowed points and bank the the "current" use year points. Dercember is a weaker use year for the summer trips, particularly if you mean August rather than June, but it still creates a better hedge than a March use year does for a December trip.
Ultimately, you may just conclude that use year choice should take a back seat to choosing the best contract in the resale market, considering price and number of points. In 19 years as a DVC Member, I have never been required to cancel a trip and likely there are many others who have also never needed to do so.. Also, the time you will usually go in the next five years or so may change as time progresses. For example, when you retire and kids are no longer in school, October to first half of Dec could well become the time to go. In essence, what is the best use year now may not be that in the future
