A tiller in my opinion is the way to go if your plots are established. One good pass and they're ready. You do have to watch out for stumps and don't get around living trees. Stay out from under their branches and you will be fine. You can move faster with a disc but if you don't have a extremely heavy disc and tractor it will take a few passes to get the ground chopped up well. A plot that is shaded may disc in nicely the first time but one that has a thick layer of grass on top will take a bit of time. I like to see pure dirt or mostly dirt in my plots. On an established plot I will take a tiller over a disc any day. I can run around 3mph with my tiller. If you do get a tiller get one with gears. NO CHAINS!