Within the Empire, it's hard to choose between Grey and Pitt. With foreign policy, either Atlee, Churchill or Thatcher. Thatcher wasn't that good domestically from what I've seen, though. But... I don't know many more British PM's either
I apparently don't know enough of the history of my own country, as I don't know half of these names. So I don't think it's fair for me to pick, as the only older Prime Ministers I know are the most famous ones like Churchill and Atlee. That said, out of the recent PMs, my pick, if a little bit of a curveball, has to be Blair. Guy was the butt of many a joke, and got us into some wars we shouldn't have been in (Guess you could say he was the UK's Bush in a way) but he seemed pretty solid with his work in the EU, and in general I feel like all my best memories of the UK were from when Blair was PM. Plus the guy just seems like someone who'd be alright to have a pint with.
Yeah, I know more about US presidents than our prime ministers. I wasn't taught about a single prime minister in school. I say there's something wrong with our history educational system (unless things have changed since then). In the last year I've tried to learn more about the prime ministers.
Definitely. As far as British history goes, for me it seems like we mostly just learned about the Tudors and World War II. I've learned a lot more of it from books and documentaries than I did in school.