It was a decade ago, but back when I was a pizza dude, I was generally happy with either $5 or a 15-20% tip, whichever was higher. It wasn't a hard rule, I'd be happy with lower tips in plenty of circumstances, but if I got that I definitely walked away feeling like I'd gotten a decent tip, and I generally try to keep to that today.

That was in the days before GrubHub and such with all of their delivery fees, the economy was somewhat less crazy, etc. I really have no idea what the economics of it looks like today.

But back then, at the place I worked, I made pretty much the same below-normal-minimum wage that waiters and such make with the expectation that the bulk of my income would be tips. The place I worked was a rarity that had their own delivery vehicle, they charged a $2 delivery fee, if I used my own car I got, IIRC 50¢/delivery and they paid for me to fill up my tank, if I used their car I got nothing extra. Normally I'd walk away with at least $20 in my pocket on a slow night, and could count on about $100-200ish on a Friday or Saturday night. Overall I probably averaged out to about $12/hour