Spearhead from Space. The new era takes off running immediately. It's a very tight alien invasion script mixed with a great performance by Pertwee. I love the Doctor doing a regeneration story now that it's more of an established element of the lore; it's happened twice now. I love Liz Shaw and her introduction to what UNIT does ("In the last decade, we’ve been sending probes deeper and deeper into space. We’ve drawn attention to ourselves."). The Autons are great. I feel the directing is particularly on point; there's one really nicely shot scene with the camera handheld in among jostling reporters all trying to get to Lethbridge Stewart in the hospital; it feels so chaotic.