I have used many different weights and brands. Once upon a time straight 30 weight was the norm. Now 5 or 10w-30 is acceptable provided it is synthetic by most engine manufacturers. The old Kohler K series and most Briggs engines were happy with a good straight 30. I had a lawn care business for many years. I ran Exmark mowers with Kawasaki FC420 and FH 500 engines along with a few Kohler Command 20 hp engines. I used straight 30 and 10w30 dino oil. Pennzoil, Rotella, Castrol, and house brand cheap oils. Never lost an engine despite the hot and sometimes dry, dusty conditions. Trust me, those engines worked hard and were at run at full throttle. I changed oil every 50ish hours and checked the oil level before I used the mower for the day. When I bought my first diesel truck, a Dodge dually, I began to use 15w40 Rotella and Supertech in my mowers.
Now I repair and rebuild commercial mowers. I have replaced 2 Kawasaki 25 hp engines that had over 3000 hours on them. Those were the highest hour air cooled engines that I had ever seen. Both from a guy who bought the mowers new and he had a 2 man crew. His secrets were to check the oil level each day before using the mower, keep the air filters "clean", once a month he ran a tankfull of premium fuel with additional carb cleaner added to it in each mower. A new fuel filter, spark plugs every season and keep the cooling fins clean of dirt and clippings. The oil he used was Mobil1 10w30. Oil and filter change every 100 hours.