I would use the Bible (if I am to be faithful with an opportunity to witness for Christ)! Why do you wish to substitute one of these books above for the Book? Even the Gospels are not the whole counsel of God.

In addition, it depends on the person's needs and even nationality. Mark is "normally" the least offensive NT Gospel to most Jews (John being the most offensive) and Romans the best NT book to minister to them with (and what of the OT? ...). In Islam you will be jumping all over the Bible, proving the doctrine of God (as Islam says men cannot conceive what God is like because He has not revealed Himself), the doctrine of Revelation, the doctrine of salvation (as Islam denies the sacrificial death of Jesus and His resurrection), prophecies come into question (as Islam claims that the Bible was changed to eliminate the Prophecies of Mohammed), etc. Of course, I am speaking of mere "beginning" points and thus the Holy Spirit could have your lead them throughout all of Scripture, before it is all finished ... Indeed, you would have to in finality answer the question, 'What is the Gospel?" for the individual.

Reformed and Always Reforming,