My favorites are somewhat fluid, depending on when I'm asked. But here are four Christmas movies or specials that I've always loved.

The Night They Saved Christmas (1984) (Free stream on Tubi)
A seldom seen movies about an oil company using dynamite in the Arctic to find oil drilling sites, which puts Santa's toy factory at risk.

Rudolph, The Red-Nosed Reindeer (1964) (Watch with ads on Youtube)
Stop motion film by Rankin/Bass. This is the one with Yukon Cornelius, Hermey the Elf, the Island of Misfit Toys and Bumble, the Abominable Snow Monster.

Santa Claus Is Comin' to Town (1970) (Free stream on Freebie TV)
Stop motion film by Rankin/Bass. This is the origin story of Santa Claus, and how he started giving gifts, despite the Burgermeister Meisterburger making toys illegal.

The Year Without a Santa Claus (1974) (Free stream on Tubi)
Stop motion film by Rankin/Bass. This is the one with the Heat Miser and the Snow Miser.