What is your favourite tank? Nice question, but impossible to answer. And a lot of my favourites were mentioned by others already.
Let's limit myself to World War II, which is my main period of interest.
If I were a tanker and wanted to survive combat, I'd go for the Tiger I or Tiger II.
If I was a general that wanted the best tanks for battling the enemy, I 'd go for the Panther.
If I was a head of state and wanted to win the war, I'd go for the T-34.
If I would go for elegance, I'd choose the Crusader Mk I.
If I would go for an interesting vehicle, I'd choose a Churchill Mk IV AVRE carpet layer with full wading gear.
If I would go for a beautiful tank, I just wouldn't know. (Tanks are not very beautiful).
And if I would let my heart speak to answer this question, I would say, with a lot of doubt, the Queen of the Desert: A Mathilda Mk II in caunter scheme camouflage. Maybe