This was one of my favorite shows when I was a kid. My first story was The Android Invasion was Tom Baker. I also remember much of the Davison era, particularly the cliffhanger of the first episode from The Caves of Androzani where the Doctor and Peri are facing a firing squad. Very memorable. I don't recall anything after that at the time, but after Doctor Who returned in 2005, I started watching as many DVDs of the show as possible.
My favorite stories from each Doctor of the Classic era:
First Doctor- The Aztecs
Second Doctor-The Enemy of the World
Third Doctor- Inferno
Fourth Doctor-City of Death, Warriors Gate
Fifth Doctor-Earthshock, The Caves of Androzani
Sixth Doctor-Revelation of the Daleks
Seventh Doctor-Remembrance of the Daleks