I visited Jordan in 2005 and whilst Petra was as you may expect the undoubted highlight, the Roman ruins of Jerash was not far behind.
I am yet to visit the likes of Persepolis, Carthage and Leptis Magna, but having been to Volubilis, Butrint, Pompeii, Baalbek, Beit Sheehan and others, I would put Jerash (Gerasa) Palmyra in Syria as the best ancient city that I have been to.
Biblical Jerash was one of the cities of the Roman Decapolis and is one of the best preserved cities from that period. The high point of the city was in the 2nd century, when it had a population of 20,000-25,000. Most of the ruins are from the Roman and Byzantine periods.
The amphitheatre was very well preserved as was the bath house, but what made Jerash special was the colonnaded ceremonial walk way. The columns were formed into a perfect arc with roads wide enough for a chariot leading from the north and south to the circular parade area.
It was very easy to imagine important dignitaries or high ranking military officers sweeping along the roadway, thronged by thousands of waving, cheering subjects as legions of soldiers lined up for inspection in the parade ring.