What engines are on these machines?
Example, B&S like a SAE 30 oil, and Honda recommend a 10w30
A multi grade will cover a broader range of operating temperature conditions, but you might find it uses more oil. Air cooled engines do burn oil, at a small rate per hour.
If it's a Briggs engine, I'd just stick with a SAE 30, if it's anything else I would go with the spec found in the manual. I personally wouldn't bother with a expensive oil, you'll still have to change it at the same service intervals anyway.
Bottom line: Just go with the recommended.