Best anniversary month for Christmas

What is the best Anniversary month to have to ARP for Christmas?

I would say September 30th end date. If you cancel the arp reservation you still have time to use the points.

I'm not sure it matters. The use year will almost certainly be re-aligned to January anyway.

A september 30th end year is the best regardless of your desired arp. December 31 is the worst as it is very busy to call in then, most have this use year, there is nothing available for the last two weeks of december last minute, travel plans are usually set for these two weeks in advance and the guest confirmations follow the same expiration date.

September 30th gives you a chance to use thanksgiving, Christmas/new Years, all winter, spring break, easter, summer and then if you still have points left then there is lots of availability for last minute trips.