I've owned the first BMW Mini and the second version; both were Cooper S models.
The first version was a lot of fun to drive but the interior rattled terribly (there was a known fault with the frame holding the dash and Mini would fix cars under warranty but even then, it still sounded like a party of mice having a disco under the dash). The engine was great if you kept the RPMs up and pushed it hard; however, the torque steer wasn't enjoyable and made getting off the line smoothly a chore.
The second incarnation is a much better built car - the interior is BMW quality and feels like a larger car. There are zero rattles and while it has lost some of the quirkiness of the original car, it is a nicer place to be.
The engine is a massive improvement and while the car drives like a larger one, it still handles very well.
If I had to choose one, it would be the latest version.
