Mine would have to be Doomsday or The Shepherd’s Boy. Face of Boe and Father’s Day are also up there. I haven’t seen a ton of classics yet, but The Ice Warriors had a couple decent ones.
I don’t know why, but I really like the music in ‘Delta & the Bannermen’. It’s a really strange mix of cheap ‘80s synthesiser and ‘50s music - for some reason I just really like it.