I would love to encounter Brachiosaurus or perhaps triceratops. I definitely would want to stay clear from any carnivorous dinosaurs that's for sure! Other than watching the dinosaurs go by, I'd have to go hunting for food of course since cavemen had to do that back in the day! I would make cave drawings as well too.
We all know I'd go back to the time when the Giganotosaurus was around. Sure it would be bigger than me, but let's make it fun: I could easily tame it and have it protect me from other wild dinos and other Giganotosaurus.