I rented a hydraulic-based tiller last spring (Troy?) and that thing was great to work with in rocky soil! No shear pins, no stalling, just forward and reverse. It was a BEAST. Shredded new ground down 6-8 inches after two passes, and that is saying something with our heavy soil.
Too bad it cost a stinking fortune. It would pay for a lot of fresh veggies from the farm market for years. I will stick with renting and my shovel. Only really need to rent it for breaking up sod, otherwise the shovel works fairly well, and is awfully cheap. I can turn over 50'x50' in about an hour or so.
-Mark
