Spearhead from Splink is a GOAT serial for the reason of comfy. It's the debut story of Jon Pertwheels as the Third Doctor and introduces Liz Shaw as well. The Brig becomes a regular cast member and it's the beginning of the earth based plots with UNIT.
It was written by Bob Holmes with Terrance Dicks breathing down his neck and introduces the Autons to the show. It's also the first colour Doctor Who. It's a bit of a classic, RTD even "paid homage" to it in Rose with the return of the famous shop-window-dummies-coming-to-life bit.
Due to industrial action at the BBC this story was filmed almost entirely on location, so it got shot on film instead of the usual studio videotape. Which means we get a nice high definition picture for once. Unfortunately this was the only time this happened, and it's the only Classic Who story available on BluRay.
Apparently the TV Movie was shot on film as well but the chances of that being dug up and dusted off seem pretty silm.