I have mostly Shindaiwa C4 engine based equipment. I use VP Racing Fuels SEF94 exclusively and the shindaiwa engines work very well with it. I like the lower tone(I'm an electronic music composer and it's better for protecting my hearing) and higher torque at lower RPM with the Hybrid 4 engines.
My favorite engine is the Honda GX25 on my MM Backpack Sprayer. I just love the way that engine feels and sounds. I imagine the Honda trimmers with that engine must be nice.
I chose the Shindiawa T344 because it made sense to have most of my equipment from one manufacturer and having separate fuel and oil seemed like a potential issue down the road for employees to screw up.
I started with Stihl Kombi 4Mix system and eventually replaced all aspects of it with Shindaiwa C4 equipment.
For me the Stihl 4Mix engines are reliable brute force single pull start. Where as the Shindiawa C4 engines are just as powerful but much more refined and balanced but a little more finicky.