which is better coal or petroleum ?

They each have pros and cons. Petroleum is more versatile but is less available locally and has lower reserves/production--it can't sustain us for as long.

Coal is more available locally and has longer reserves/production. We can sustain energy demand longer on coal than on petroleum. It's not as versatile a fuel, however. For example, it's difficult to use for transportation (unless electric vehicles are more widely implemented).

Burning coal usually has more dangerous air emissions than burning petroleum but not always. Modern techniques such as coal gassification and pulverized, low-sulfur coal combustion with stack scrubbing can drastically lower emissions.

Coal, cause we have a whole lot of it.

petroleum,because it is a liquid