1. Peter Davison
As this story is the first of the series that was filmed (they were recorded out of order; Castrovalva was actually the fourth) it features Peter Davison's first real performance as the Doctor. You can sense he's trying to find his feet in a part that will ultimately make him a part of Doctor Who history, but this doesn't appear to daunt him as he wanders down corridors and fiddles with TARDIS controls like a true pro. Before I bought this DVD I hadn't seen much of the Fifth Doctor's adventures but it didn't take long to convince me. He'd won me over long before the episode had finished, but there was one scene which fully secured his place for me as role of the Doctor. In part four Monarch accuses him of meddling with his surveillance equipment. In truth the Time Lord has indeed been putting them out of action ever since he's discovered his Dastardly Plan, but he replies, "I wouldn't dream of interfering with your monopticons" without so much as an eyelid batted. In my opinion any man who can say a line like that with a straight face and manage to retain even a bit of dignity is nothing short of Time Lord material, and it's worth watching Four to Doomsday just for that line. And having said that, I hope I've persuaded some cautious individuals that it really isn't all that bad. There's something to be enjoyed in any episode if you pay enough attention. Hmm, now where did I put my copy of Timelash...?