Earth must be aerated in order to grow crops, and it is this necessity that brought about the invention of the tiller. Once a human-powered wheel with simple construction, this device has developed into a wide variety of efficient power tools. Today you can find tillers to suit almost any task, from simple rooftop gardening through churning hundreds of acres at a clip, from a number of quality manufacturers, such as Troy Bilt, Honda, and Mantis.Generally you can find tillers in a number of sizes, and it may help to understand the power ratings and range of each before you buy. Handheld versions use regular gas, include integrated simple controls, and operate at low speeds--generally 200-300 RPM. Many of these are quieter than other landscaping tools and emit fewer fumes and other hydrocarbons.
Larger tillers come with substantial engines and can generally turn far more earth in a given time frame. Although they are still hand-operated, they weigh a good deal more, use hardy chain drives and generate significant horsepower along the way. For bigger tasks or anything that will require considerable attention before refueling, the mid-size series is a good bet to get the job done.
Finally there are the full-size garden tillers. These generally boast larger blades, twice the horsepower of mid-size tillers, and a number of features you won't find anywhere else, including several forward gears, reverse and counterweighting. Big jobs and stubborn earth often requires the extra horsepower.