the prices don't depend on the actual company. they actually depend on other things, like if there are other gas stations to compete with in the area.
but i agree, esso's gas stations have good service. they have pumps with tv's and everything that tell the news and stuff...but one thing, their carwash's SUCK!!! sunco has the best car washes.
as for which is best for your car, i personally do not know FOR SURE...but shell claims that their gas helps clean your engine, but i doubt it's true.