It would be easier to terraform if it were at the earth's distance from the sun, either opposite the earth or perhaps in a Trojan orbit relative to that of the earth. Moving Mars with rockets would take unpleasantly long - hundreds of millions of years according to some preliminary calculations if it were feasible at all. Here's how to do it in a some tens of thousands of years. The orbit of an asteroid that crosses the orbits of Jupiter, Mars, earth and Venus would be chaotic, i.e. small deviations in initial course have large effects.
Chaotic systems are inexpensively controllable if one is in a position to provide external forces.
Our tame asteroid passes by Jupiter, Mars and Venus repeatedly. It transfers energy and angular momentum between Mars and these planets. We need both Venus and Jupiter, because both energy and angular momentum must be conserved. The orbit is supposed to be such that only very, very small delta-v s must be infrequently be applied to the asteroid to keep it in the desired orbit. If you like analogies with fundamental physics, you can regard the asteroid as the carrier of an exchange force among Mars, Jupiter and Venus.