I have an October UY and works great for us so far... our repeating disney trips seem to occur in October and March/April.
So, if you are searching for resales, I'd probably look for Aug, Sep, or Oct, but would prefer to get Oct.
Reasons: If you booked a ressie for Oct and had to cancel, you'd still have your full year (or close to your full year) to use or bank the points. If you had a Dec UY and had to cancel your Oct trip you could be in the situation where the number of points you could bank would be limited.