I have the latest shape (9n) TDi PD Sport (with the 1.9 engine). Its such a good car. I think it borrows more heavily on design from the Mk5 Golf (exterior, dashboard, console, seats etc) and hence is a bit more 'upto date'.
Spec on the newer Polos is excellent (mine has Sports Seats, Alloys, Climate, 6CD etc) - I did look at the older shape (I like the shape) but found that it would soon look dated (and lose more value ??) as newer cars tend to look more and more like the 9n.
Engine wise it is spot on (I got 61mpg over a 400 mile journey yesterday at 70-80 although with quite a lot of slower traffic jam stuff as well).
My only complaint is the hard ride on the Sport model - can get jittery around town but does make it more chuckable.
I might have to change mine for a Bora TDi soon (need the bigger boot). So if anyone wants to swap a newer (52 reg) Polo Sport for an older Bora SE (Y reg ??) send me a PM ...