IN buying a used vehicle, considering same YEAR MODEL(1998-2001), SAME MILEAGE (80k-100k), SAME UNIT BRAND and MODEL. What would be a better choice, A GAS UNIT or DIESEL unit?

My friends prefered a GAS unit since we are ALWAYS or 100% sure of the ENGINE CONDITION (even if it will be checked by a mechanic), trouble shooting GAS Engine is easier and cheaper compare to Diesel Engine. Tama ba ang LOGIC?