I like the look of the 06's better myself. Thats what I have. And if you got the supercharger you can always add the turbo. you go the other way and you have no supercharger.
07 R56 has better gas mileage looks are an acquired taste compared to the older mini, and the r56 is cheaper to make as they have made lots of costcutting but if you can get one for the same price and gas mileage is important (ain't for me and I live in the UK where it is $10 a gallon!) then get an r56. R53 are tried and tested tho !