Both can be and are true. Some people are motivated by pleasure (getting to know Jesus, for example), others by the avoidance of pain (avoiding eternal punishment). Frankly, it is not the Christian's job to ascertain the often deep and subconscious motive of each person. We are to simply present the Gospel in its pure form. The Gospel is pure gold, and able to save to the uttermost. Paraphrased:
--God created a perfect world
--Into which, sin entered
--Sin demands a wage, a penalty
--That penalty is death: a death sentence
--We all inherited Adam's sin
--None of us, not one, enters Heaven with even a spot of sin
--God offers us a substitute, a Savior, who will take the penalty for our sin (bear our punishment)
--To be saved, we must believe and confess Jesus Christ
That's it. That's the message. Simple, profound and beautiful!