I use fuel burnt. I think miles fails to take driving conditions into account, whereas total fuel at least counts idling, and gives SOME (probably not enough) greater weight to stop-and-go driving than cruising at 55.
Miles certainly takes more pertinent factors into account than time. I'd only use a time-based interval if I knew mileage wouldn't be enough to necessitate an oil change. (E.G. My girlfriend's mother drives only a few thousand miles a year so I'd change her oil annually).
As far as my car - the last OCI was 200 gallons (turned out to be 8,320 miles), hoping the UOA comes back clean with some TBN left so I can extend to 250 or maybe 300 eventually.