Suggest you read the help files and other info on "read errors".(C1/C2, PI/PIF) Scandisc tells you how well your drive can read a disc. Another drive may give a completely different result. Any errors reported do not physically reside on the disc, but occur in the reading process as a result of the drive's error-correction scheme (or it's failure to correct). General conclusions might be drawn about the disc quality as a result of these tests, but nothing on the surface of the discs is being measured. Tests like ADER/ATER and Jitter do measure a small part of the disc's physical characteristics, but these are just part of the puzzle.
There is no "best" test, no "accurate" or "inaccurate", they're all just different tools for reporting how well drive A can read disc A.