3. Peter Davison
Peter Davisons final serial, The Caves of Androzani, is quite possibly my all-time favorite of the Classic Who adventures. The Doctor and his gorgeous yet rather insufferable American companion Peri Brown, played by the very British Nicola Bryant, are mistaken as weapon smugglers and arrested by the Androzani military. They escape from custody while awaiting execution, but not without the both of them being infected by an indigenous toxin. The Doctor manages to find the antidote via bat milk, but only managed to accumulate enough for Peri. The Doctor struggles to regenerate, again hallucinating past companions begging him to pull through; however, unlike the case of Tom Bakers regeneration, the Master appears as well to taunt the Doctor and convince him to go quietly; it is only with this final push (and apparently the sight of Peris breasts) that causes him to pull through to see another day as Colin Baker.