If you are mantaining an edge, I prefer a shovel rather than an edger. Edgers create lots of loose soil that has to be raked around or removed. Edgers are great if there is no existing edge, and leave a nice flow, but require a good bit of hand work after you edge to get a smooth, natural look. In most cased I don't think an edger saves a huge amount of time but will definitely with some effort, give the best final product.
I use a Edger Hoe>> it has a flat wide head and can be turn sideways to cut deep and make a smooth cut along the bed , this tool is faster then a spade and less dirt movement. Good for small and medium beds <> larger I use my bed former> I made these tools<> Bed Former is B&S 6hp with blades adjustments to form edging.
a spade is the best way but it takes some more time...also in order to keep it looking clean and crisp, i like to use a hand held bed trimmer. its made by sandvik and it looks like a giant pair of scissors on long handles. it may take longer than weedeating but for that personal homeowner touch...it cant be beat!
I use the bed edger on new beds and keep them looking good throughout the year with the trimmer. If it needs it the following year I will use the bed edger again but it will be $1.00/foot. I don't have the time to use the shovel or anything else and they don't have the money either!