| I haven't got both, but I have got the R56 "S". It all depends whether you want rare but extremely fun car or want a mature MINI that is refined but very fun! Owning an R56 "S" is a pleasure, even in run-in because there's so much poke at lower revs.
You've also got to consider looks and get the right car for your driving style where you will enjoy it the most.
However, I quite disagree with GBMINIs blog post. It doesn't surprise me however as I've read alot of R53 owners that have gone to the R56 have been disappointed. I can only imagine BMW have made the MINI grow up to attract more customers. It's certainly grabbed me in comparison to a choice of cars I could of got (Focus ST, Astra VXR, Leon Cupra, Mazda RX-8).
I do remember driving an R50 Cooper when I did my pass plus. To be honest, I don't think the R56 has lost any connection with the road in comparion. I can chuck my R56 "S" around corners with ease and know wherever I point my steering wheel, it'll go there. It still has that go-kart feel no other car can give you. I guess the electronic assisted steering (not sure if that was in the R50) may have a lost that feel a little bit, but the MINI won't stay the same. It has to go in some direction, regardless of possibly BMW coming away from the Mini original a little bit with the R56 to make a better all-rounded car.
As a an R56 "S" owner, I can only offer the positives the car as I definately feel it's a good progression from the R50/R53.  | 
