Hmmm....I think I've had them all. I've worn out several Sears ones, a couple of Ryobi, a John Deere and currently I have a Troy-Bilt TB70SS.
First and foremost...Buy a Straight shaft!! I will NEVER own another bent one..kills the back.
The Troy that I currently have is the easiest to start than any that I've ever had. The string part is a bit confusing though because it uses the "split" string. Not bad though. It has good power and is fairly light weight. I can weed eat for several hours and I'm a 5 foot, 110 lb. woman. Overall, I'd give it a good rating.
The John Deere..I tore out the shaft twice...not good. Loved the great saw blade that I could switch out though. It was a bit temperamental when it came to starting, but I could usually get it running without DH's help. Didn't buy another one due to the insides of the shaft breaking so easily.
The Ryobi was a great started...but I wore it out in 1 year. Great power though and I liked the design where we could switch out the heads.
The Sears ones...I wouldn't walk across the street if they were giving them away for free.
Having said all that....the very BEST weed eater...even better than Billy's goats is.....Round Up. :D