They're both really fast, at 18 frames per second because they both access the same point.
Direct Scan is OK for what it does. Quite similar to Powerlogger but NOT the same. Not sure what BobbyBuick is referring to when saying Direct Scan has more options??? And I have to correct one thing he stated. DS does not use a serial port, It actually plugs into your computer's parallel printer port. So your computer needs to be fairly outdated, and running win98SE or older.
Options? You can't really beat the Powerlogger with it's analog input device that will accept and log inputs from a variety of external inputs in adddition to all the data being read directly from the ECM.
Fast? both the same
Supported? DS no PL yes