I honestly thought the One would trouce the 500, and was very surprised to see the 500 post a quicker lap time, as the MINI does have a very good chassis. Perhaps the 500's optional wide tyres gave it the extra grip required?
Having driven MINIs (and Minis) over the years, I currently own a new 500, and can say that the 500 is a better proposition for a "very small" car than both the MINI/Mini. The MINI is really too big to make any direct comparison (should be compared with Golfs, etc), and the Mini is unrealistic for modern use as a 2+2 (in fact we sold our Mini 30 to make way for the 500). They are very different cars aimed at different things.
Let's be honest - the "battle" is really about "how superficial are you about wanting the latest chic accessory". The 500 wins that one no sweat. My wife
is that superficial.
The 500 has a NCAP 5* rating. Not that it means much, as these ratings are all too contrived for the real world, but if the worst happens it's impressive for such a small car.