Personally? If you aren't running it much, I like a full synthetic. You could also use it on your car or other equipment.

Amazon Basics High Mileage Motor Oil - Full Synthetic - 10W-30 - 1 Quart - 6 Pack https://www.amazon.com/dp/B07C5QWHN6/ref=cm_sw_r_apan_glt_fabc_K5P3FH7S6759HR6X0NJV?psc=1