Petrol over diesel anyday, its a false economy buying a diesel because of the mpg.
the diesel in Ireland has high water/sh*t content combined with the majority of irish peoples lack of proper maintenance of their cars results in problems with pumps, injectors, turbos, dpf's ( soon to be NCT and DOE particulates test) all big money.
in saying that the 2 cars you mentioned depending on history and condition i would take the diesel.
the 1.4 golfs of that year are oil guzzlers if not well maintained from day 1 and if mileage is over 100k miles many face emissions problems in NCT due to poisoned cats etc.
you will know on cold start if it was minded, they are very tappety if oil changes were not regular all along.
i sold a 99 golf 1.9tdi (not PD) last week with 230k miles on it, going like a bomb. had it since 2 years old well maintained.
never had any engine work except 3/4 sumps and a clutch at 190k miles.
original turbo/pump/injectors. they are bullet proof if minded.