I'd look at my budget and figure out where I'd get the most for my money. Also, it depends on what you'd be using it for. Ideally, I'd go for the FN2 or Mini over the Mk5. I figure that the FN2 would probably feel the most special of the 3 and because they are bit of an ugly ducking, they seem to be pretty good value from recent internet searching.
My mum had a nearly new Mk5 GTi and it was a good car but it never felt particularly special (compared to thinks like the Clio Trophy she had) and they are little long in the tooth now.
Before that she also had an R53 Cooper S which was good fun . I've not got any experience with an R56 but I'm sure @NurseHolliday should be able to give loads of info.
Finally, I've no direct experience with the FN2 but the one of the last cars I owned in the UK was a DC2 Integra and it truly blew me away and indoctrinated me in the ways of Honda. Even at the age it was, it felt like a precision instrument and always exciting.