Either start with Rose. Or start with the first episode of Capaldi. Either way, you can work your way back if you want to. Just be aware that Capaldi is intentionally playing him rough for the first several episodes.
But my gosh I like his attitude better than the last two (teen girl) doctors.
ETA: The companions Capaldi starts with, the three in Georgian London. They’re amazing recurring characters who really could have their own show.
