I work on 2 and 4 stroke engines for a living, and the 4 strokes in the Ryobi, troy-bilt, and CC trimmers are really really BAD engines. The valves require regular adjustment, the carbs are non-adjustable, the vibrations are terrible.. We see at least 1 a week that is a year old or newer that has failed the owner. The bevel gears are noisy and wear fairly quickly.
I do not reccomend a ryobi 4 stroke (be it badged as a cc, troy bilt, ryobi, or other MTD brand) to anyone, based on the number of problems I see with them.
As far as Stihl goes, they are expensive, and while they do seem to work well, they feel clumsy and cheap, I really dont like the air filters the use, nor the handle styles, alot of customers tend to agree with me on thse points, we see a few stihls a week, ranging from new to 5 years old, usually it's a carb problem, sometimes something else.
We sell ECHO power products, and as far as blowers, and Trimmers go...They have all other manufacturers licked. Perfect anti-vibe handles, great air filtration , perfect balance, serviceable bevel gears that remain quiet and donw whine. Quiet mufflers, smooth recoils and the best warranty in the industry, as well as a lifetime guarantee on the drive cable and ignition coil. We have quite a few come in for annual service, many are used daily by contractors and landscapers and many are on their 3rd or 4th trimmer head from such extreme use...but still blow new compression and run like sewing machines!
Just my reccomendation...take a look at an Echo SRM-230 or SRM 210, and dont be fooled by the small displacements (21 and 23cc respectively) they make excellent power and I never hear any complaints from owners and users alike.
Cub Cadet on a trimmer is just a sticker on some other trimmer. An ECHO is an ECHO.