I prefer to redline with artillery, then use the tanks, because I want the battles to get lotsa elite tanks, resulting in armies. Nothing better than 4 armor units in an army to take down nearly anything. No better defense unit than an army of elite MI's, either. I love my armies full of elite units, as they gain that extra move from being in an army. And for a "race to Baghdad" situation, user radar artillery to redline all defenders, take the city with tanks or MA, move on, repeat until you run out of units, resume next turn. Even a country defended by MI's can't take that for long.