As ever, check the APR (the interest rate). There are some good deals for personal loans at the moment from a variety of banks/building societies.
Personal loan = car is yours, to do with what you like - so you can sell it without having to pay the loan off.
Mini Select (and Hire Purchase) = car is not yours, so you need to deal with Mini Select if you wish to sell the car.
One advantage of HP is you get some more muscle to help you if there are problems with the car. HP companies will lean on the dealer/ mini uk to get things sorted.