Shell Rotella T1 SAE 30 is about as good as it gets. It has no S rating anymore but still carries a C rating for 2 stroke disels. However a small engine will not care.
Shell Rotella T5 10w-30 is perfect for OPE in my opinion & practise. Certainly nothing wrong in using that T1 conventional 30 weight as mentioned above.
10w30 synthetics work well in place of sae 30 since they don't require many if any viscosity index improvers. if you want something a little better, Mobil 1 High Mileage 10W30 has a good additive package for any lawnmower.
All above suggestions are fine, but my 2 cents is that I run a small engine shop, and use almost exclusively ST30. Have been putting it in my own and customers ope for many years.
I use valvoline fleet 30 weight. It pours better at room temp than any other conventional. I suspect it's a 10w30 marketed at straight weight. The label reads "great for gas and diesel" though it carries no gas certs.
I use Rotella T6 5w-40 synthetic in all of my mowers and mowers I work on. As long as the oil is kept at the proper level and changed per useage, brand of oil is really a personal preference.
I've been using PYB straight 30 for decades without issues. When QSGB straight 30 goes on sale, I'll use that as well-it's actually got a strong green tint to it (not that it matters-just reminds me of some older spec oils)