The key component of a garden tiller is the tine design.  Tines are the metal prongs that work and loosen the soil. Their length and position determine how the machine operates, how far it can cut into the soil, and what kind of soil it works best in. In some cases, short tines are sufficient, but for other jobs, you need tines that dig deep. Here are some differences between tillers with rear tines and those with front tines:
Rear tines: Machines with their tines in the back typically do a better job of breaking up soil that has never been tilled and cutting deeply into dense, thickly packed dirt. They have large wheels with deep treads and adjustable depth regulators, so you can till to different depths.
Some rear tines are counter-rotating. Because they move counter-clockwise, they give you even more control to handle the toughest dirt. These tillers create the least vibration when cutting through clay and rocky dirt, and they are great for creating new garden beds where they didn’t exist before.
Mid-tines: Generally, tillers with tines in the middle are the easiest to control and move while the machine is operating. The rototiller’s engine is usually located above the tines, giving it better weight distribution.
They are less powerful than rear tines and more suited to light maintenance work than creating new seed beds.
Front tines: These tines sit before the wheels and rotate forward. Front tillers don’t cut as far into the soil and aren’t as effective at breaking up tough, clumpy dirt. Front-tine tillers generally cost less than rear tillers of comparable size and power.
They are much easier to maneuver over dirt already loose and don’t require much work.