Is a petrol or diesel car better value?

What’s better, the petrol or diesel Peugeot 308?

Is a petrol Toyota Yaris good for motorways or should we switch to a small diesel car?

My grandson commutes 64 miles each day on mostly motorways. He has a 2016 Toyota Yaris petrol with 44,000 miles on the clock. Would you advise him to change to a small diesel car or to stick with the Yaris?...