I went Airborne. It's the tree I know best. My problem was I got behind the curveball so I was using resources just to build the basic infantry and engineers needed to operate. By then, I rarely had enough manpower to produce the airborne or anti-tank to drop in behind the enemy line. Of course, this only works against more than one tank when you have the front lines to keep the tanks occupied. If not, it results in what happened to me.. when you finally drop the AT, it's getting pummeled by a tank before it gets set up.