Buying Used: Which VIN Check Company Is Best?

Not a one of them is worth a lot. They may be accurate in the title transactions, but that is it. There is no central clearing house that anyone is required to report repairs to. Large rental companies are mostly self insured and do their work in house with no public records. If I bang up my car, have Billy Bob do the repairs, and pay for it out of my pocket, there are no records.
If you want to use a VIN report fine, it will at least give you the title history, anything else on the report should be considered a bonus. In no way should you consider it a complete history.