I looked at the VW UP Ruby along with the Polo and the new Hyundai i10 when I was looking for a small motor. The UP was the first to come off the list as theres been a fair few complaints across the forums on gearbox noise/chattering from new for which VW says is normal and don't want to know. Listening to some of the videos posted up it put me right off. Depends on your budget really but the new i10 is worth a look if after a smallish car, its gets great reviews and bit of a bargain, when I was looking though at the time there was a 5 month waiting list. Polos and MINI's will obviously be more expensive. Suzuki Swift 1.2 is worth a look, just as acomplished as the MINI but cheaper, the Sport is little gem. POLO is still one to go for but not the 1.2 as painfully slow but then larger engines and the prices go up. MINIS are great for residuals and handling but little else and expensive in the first place.
I would have a Ford KA over the FIAT 500 as they're the same car but the Ford is tweaked much better for ride and handling.
Tim.