Homeowner here. I'll throw in my 2 cents...
Gas and it doesn't matter the brand. I know, some will spout "Heretic!"
Seriously, if your a homeowner willing to take care of your lawn, kudos to you! Your neighbors (and local real estate agents) appreciate your efforts. Electric is great if you have postage stamp size lot and a 50' extension cord. But that damn cord is constantly in the way and the life span of the wacker is limited as the motor is cheap and the housing isn't sufficient to protect the goods inside. For the one or two times you may use it for a VERY small yard, it's OK. The battery powered ones, eh... again, for small sized lots (make sure you pre-charge that puppy).
Gas, 2-cycle has it's pros and cons too... pros: go anywhere and power! and can be relatively easy to repair yourself, extending it's life unlike electric which break and are chucked. Cons: shakes like a mother when unbalanced, can be noisy, needs fuel and 2-cycle oil (obviously).
Brand? How much money do you want to spend? That should be the question, right? I mean, if you are a pro, using the trimmer constantly, then of course you're going to want to get the best you can (and it's also a tax write off I'm guessing...). If you are asking as a homeowner, consider that you'll use once a week (maybe).
For me, I fixed a neighbor's garage door a couple years ago; as a 'thank you', she gave me her old gas powered trimmer, Home Depot "brand" Homelite. Yes, it was probably around $100 new; hers was a few years old, used sparingly. I used it a couple times and the shaft sheared off. Later, the linkage to the throttle busted. I purchased a new shaft ($70) and rebuilt the linkage. I also purchased an upgraded spinner head ($30). So, the free trimmer was rebuilt/upgraded with $100 and an hour's time. Works like any other gas trimmer and starts every time. I use it once a month in the summer. No complaints. Sure, it's not a Sthl or Echo, or whatever; but it fit the budget for my use and property size (1/2 acre with a 2,200 SF home).
I hope I didn't stray off topic here...