Honda HRX Versamower.
1st year I used the oil that came with it (I think it was Honda 10-30 but not real sure; was a little red bottle).
2nd year I used Shell Rotella 15w-40 that was left over from one of the motorcycle oil changes. Later I changed that bike to Rotella 5w-40 synthetic, so then I used the left over for the mower again. It did swell last couple years.
This last spring, on the other motorcycle, I switched it to Amsoil 20w-50, so again I used left over for the Honda mower. I can't believe I'm using Amsoil for a mower, but I like it in the Harley, I figured might as well.
I already bout Amsoil for the spring change on the Harley, and I'll use it also for the mower again.
My mower gets better oils & changes than some folks I know use in their cars & equipment.