When buying a truck what is suggested better for fuel gasoline or diesel and why pls?

Depends on what you're doing with it. If it's just going to be a personal vehicle, gasoline will be just fine (plus, you usually can't find a diesel engine option for trucks under 3/4 ton in the US). If you're going to be using it as a work truck, pulling heavy loads and such, then definitely diesel. It delivers low end torque, and is more efficient overall.