As above, petrol if you are doing shorter journey's as a diesel will not get remotely warm and this will lead to big running problems further down the line. That's before you take into account the higher cost of diesel and poor economy you will get.

We had an 07 Saab 9-3 1.9 TDi (pretty Vauxhall Vectra) which was bulletproof when doing a 70 mile per day commute, then the ex-wife changed jobs to be 4 miles away but insisted on still using the car, within 6 months it needed the EGR valve, DPF and inlet manifold all changing because they got horrificly clogged up from the short journeys. Very bloody expensive they were too!