Assume you have all the luxuries of a modern life in your Tardis (toilet, hot showers, TV, books, game console, ...) which doubles as a mini self-sufficient apartment with it's own energy stores and generation.
Where in history would you go if comfort wasn't an issue?
I'd love to witness the Chixilub impact. Or Pompeii, or any huge natural disaster. The bigger the better. I'd also like to figure out how the moon was actually created. Then see the sun swallow the earth at the end.
Those last two might require some careful planning on where to be to witness those events safely