Plain and simple, multi-viscosity oils are not necessary unless you plan to operate when outside air temperatures (cold engine temp) are below 50 degrees f. If you plan to run it when colder than that, use 10w-30. This comes directly from the engine manual from your engine.
As for synthetic, it isn't necessary either. Small engine oils are specifically formulated for small, air cooled, engines and therefore using anything else will likely show you no noticeable improvement in how the equipment runs.
Routine maintenance in itself, is so much more important than what oil you run. I have a Briggs V-twin with over 500 hours on it, always gets Briggs Filter and Briggs SAE 30 oil and after each summer the engine has not burned a drop of oil, and it is still golden yellow/brown after 50 hours of run time. I flush the oil with every change and I only run non-ethanol 90 octane, but I do that with ALL of my.small engine powered equipment.