The MINI Cooper S is a fantastic car!
Here is a collage of images from my former beloved Celeste:

I switched from the MCS to my Prius 'Elettra' for a numer or reasons:
My MCS had some quality issues, but I would guess that MINI has sorted all those out.
In 2 years - 40k mi,, I had about $8k of warranty work done: new speedo, window winder motors, steering column, tranny throwout bearing...
I didn't want to get stuck with that after the warranty expired, so I decided to sell. Then the question was: another MCS or the Prius? If the MINI One Diesel had been available in the US, I would have considered that as well.
Well, I decided I should be good and get a frugal (gas) car.
The cost of both was about the same to me.
MILEAGE:
here's an important consideration:
though the MCS is listed as 25 city 32 Hwy, I never got close to that. Initially I managed to average 28 mpg, but later that dropped to 26, then 25, then 24. Why? Because the car was so much fun to drive! That was the problem for me, it enticed me to drive it like I stole it, and I burned lots of gas. I had it at the racetrack a few times and managed 8 mpg! I am convinced that half the difference in mileage between the MCS and the Prius II is the driving style: for the MINI it is very spirited, for the Prius it is granny style. This is also a safety consderation for me. The MINI was probably a safer car, because the handling was so much better, and I don't even want to think about evasive maneuver handling in the Prius: just don't! However, in teh long run I think for me personally teh Prius will be safer because I drive so much more sedately and non-agressively, and I am glad for that!
Now I am close to averaging 50 mpg in the Pirus, vs the say 25 in the MCS: twice as much! Do I love the Pirus? I love it and feel good about driving it. Do I miss the MINI: you bet I do!
They are both great cars, and surprisingly the MINI had more front room than the Prius, and much, much better seats, and an infinitely better stereo (the Harman Kardon, well worth the $500), but the suspension was so stiff that my wife did not like riding in it very much.
Cheers,
M