My latest weed eater purchase was to invest in a Sears battery powered weed whacker and I am really happy with it. It's a lot better than any gas model I've owned because of the weight difference, the fact that I don't have to screw with engines being hard to start, mixing gas and oil to feed it, etc. The model I bought is the 40 Volt Lithium battery Max model. Now, having said all that, I should tell you I bought it 3 years ago, and this past year had to replace the cowling that guards the string and keeps it cut to the right length for trimming, and I also replaced the spool. Both purchases replaced worn out plastic parts, and it trims every bit as well as it did when brand new. Those parts only cost me like, 20 bucks with free shipping from Sears Parts Direct, which is usually the most expensive way to go, but for some reason these were very reasonably priced.
I would definitely go with this string trimmer model (I keep about 2 acres manicured so I bought an extra battery) over any gas powered string trimmer. The old WeedEater Featherlight trimmers (which they don't make any longer) were half way decent gas models, but none of any of the full sized gas trimmers I've tried are nearly as good as this Sears battery powered unit in my opinion.