December is the best because points would be available 1 month early so come January when the 11 month window opens for the following December the points are available, correct?
as i said above:
remember that UY has nothing at all to do with when you can call to book.
here's a long explanation:
remember that all of your pts through 2040 and beyond are already added to your account when you buy the contract. you can call at 11 months out based on your home resort, not UY.
so you really have a couple of issues limiting you:
1) UY tells you when your pts are valid for stays.
so for a silly example, if your UY month is dec, then your 2020 UY pts are valid for stays from dec 1, 2020 through nov 30, 2021.
2) you can only bank ahead one year or borrow from one year ahead. and once you bank or borrow pts, they cannot be moved again.
so if you borrow your 2020 pts into 2019, they would be valid for stays beginning on dec 1, 2019. but your 11 month window for dec 1, 2019 doesn't open till jan 1 (or so), 2019, so your 2020 UY pts are not available for booking until that point.
use year month is mostly an issue if you need to cancel.
some examples:
if you have a feb UY and a dec 2013 trip and you need to cancel 60 days out (in oct 2013), your banking window for your 2013 UY already closed on sept 30, 2013 so you'd have to scramble to use all of the pts in the reservation before they expire on jan 31, 2014.
if you have a dec UY and a dec 2013 trip and you need to cancel 60 days out, your banking window for your 2013 UY won't close until july 31, 2014 so you'd have until then to decide whether to use current year (2013 UY) pts for a reservation in that UY or else bank them to the next year. (you'd still need to use banked and borrowed pts by nov 30, 2014. as stated in #2 above, you can only move pts one time.)
if you have a feb UY and a dec 2013 trip and you need to cancel 5 days out, the pts would turn into "holding" pts so you'd have to use all of the pts in the reservation subject to a 60-day-out limitation - but that won't matter much since they expire on jan 31, 2014 anyway...which is less than 60 days out.
if you have a dec UY and a dec 2013 trip and you need to cancel 5 days out, the pts would turn into "holding" pts so you'd have to use all of the pts in the reservation subject to a 60-day-out limitation - but at least you'd have 12 months before they expire on nov 30, 2014 to decide what to do with them.
that’s the long version of how UY makes life easier or tougher if you need to cancel – try not to travel late in your UY if you can help it.
more info about UY is here if you need it (you may want to bookmark this thread for later reference):
http://www.disboards.com/showthread.php?t=1942668