Which is the best weed eater to use for my yard?

This is the winner, in my opinion is the Black and Decker 18 volt cordless weed wacker!  My neighbors are always borrowing mine!   No bumping or turning off the motor to hassle with hand feeding string; Black & Decker's 18-volt cordless string trimmer features the company's exclusive Automatic Feed Spool (AFS) system that automatically advances cutting string without bumping. By letting centrifugal force feed the trimmer line as it is needed, you get a smooth consistent length of line for optimal performance.Battery-powered, this cordless string trimmer has the capacity to trim grass after mowing for up to a 1/2-acre home site on a single charge of both included 18-volt batteries. Quiet and easy to start, the unit requires no gas, oil, or tune-ups. The Grasshog's Groom 'N' Edge head rotates 180 degrees to convert the trimmer to an edger with a push of a button. When used as an edger, the flip-down edge guide keeps the Grasshog in line with sidewalks and driveways. A secondary handle adjusts for increased comfort and control. A lock-off switch prevents accidental start-ups to ensure safe usage every time.

I also listed a 12-volt version, but I would pop for the 18-volt