Let me add to my earlier post in that you probably don't want to go deeper than 12" with a subsoiler so 45HP in 4WD could do that with one shank in my soil. I do it. On the back of my 80 HP 4WD I can pull that single shank with ease and could probably pull 3 shanks at 12" deep. I use a chisel plow almost all the time and use the subsoiler once a year or every other year to bust any hardpan.
It more depends on the soil and the amount of clay. Gravel soil doesn't really compact but jumping up and down on clay probably does. My vote is chisel plow.