Diesel or petrol v milage

Hi i was wondering if someone can advise me. We are looking at similar old models of campr van. One is diesel with 150,000 miles and the otherpetrol 88,000 miles. I know diesel generally lasts longer. If the condition and model is pretty much th esame are we better going with diesel or petro. Both are similar engine condition re servicing etc. thanks. Sorry about the spelling, typing this on a tablet which doesnt let me view and type at the same time!