I know you already made your purchase, but to anyone else who reads this thread, I vote for Stihl.
I used stihl trimmers at the golf course I worked at for 4yrs (worked there for 5, but they bought a stihl after my first year). There were some weeks I weedeated 40hrs. (lot of ditches, trees and pond banks). I even dropped it in a pond once. Ran like a champ. I probably averaged 10-15hrs/week/year
Later, my parents bought it and after 6-7 yrs of use, it still works great! (yeah I weedeat their yard)
It was the model prior to this one.
http://www.stihlusa.com/trimmers/FS55R.html