Dont spend money for toughness. Your not going to get anything that wont scrape off on rocks!.
Priorities...
SURFACE PREP...So it dont "fall off"!
Cheap...Wally World or Similar
Easy to touch-up...Textured paints can be rolled or brushed, so no masking needed and touch ups blend good
Looks...Shiny looks/cleans best. Appliance epoxy best I found for this.
Now, my vote for the best, most durable coating, if ya wanna spend some $$?
Good quality Bed Liner! My tires wont even scrape it off my fenderwells where they rub. ( I think it took three years to finally start to rub thru!) It will not rock chip, although I would imagine you can still "rock scrape" it off! I got a Jeepin buddy who painted his entire GPW with it. I dont think I have seen any scrapes on the body yet! And its holdin the rust together!! LOL!