In my opinion the petrols are more reliable than the diesels. In general that is. I know there are exceptions.
Economy wise i would forget the TDV8. The TDV6 might be worth considering though.
Like everything in life, its a compromise. Theres pros and cons to each of them. It really depends on what the vehicle is used for and how it tends to be driven..
Edit: the performance of modern diesels is great, but it comes at a cost - they just dont give the real world fuel consumption figures you expect from a diesel. They are also pretty complex.