Most of the rentals I have done has been choc's off/on
tiger club when I was there did it tacho + (think it was 0.2 for the cap10 which they then reduced to 0.12 but put up the hourly rate)
Tacho I think is generally fairest as you can run around at 2200 rpm and pay less than running around at 2400 rpm.
I think chocs off/on or hobbs just encourages a pilot to run at 2500 rpm to get where he is going quicker and save money that way leaving the school/owner facing with higher fuel/maintenance bills