I've got a Stihl model that runs interchangeable attachments, though I've only got the string trimmer and a brush cutter head. It's about 5 years old and is a dream to start. I also have a small Dolmar string trimmer that's about 10 years old, and though it's too small and underpowered for anything but light use, it's been a good, reliable machine. It replaced a Ryobi string trimmer that never seemed to start well, or run well.
You'll probably hear this over and over, but always use fresh gas, and keep a few fuel filters for all your small engines on hand. The ethanol that is now in gasoline attracts water and sinks to the bottom of fuel containers. The water/ethanol will also collect in the fuel filter, so replacing them will help immensely. I use the Marine-grade Stabil (ethanol formula), and I shake up my (gas) can before filling my string trimmer, chainsaw, etc. I'm also a believer in using name-brand --Stihl, Echo, whatever-- 2-cycle oil, and not a bargain brand. Of course, don't use last season's fuel. You can mix it in small amounts into your vehicle's tank to get rid of it.