Question: I messed up with my trackpad settings. I am also using bettertouchtool.

The problem is three finger drag has completely stopped working. None of trackpad settings in system preferences or options under accessibility are helping. 

Is there any way I can reset trackpad settings to original, the way it came with factory. I tried resetting PRAM, not helped. Any way to get back the default trackpad settings.

Answer: 
this is what I did:

* uninstalled BTT
* entered in Terminal `mdfind -name bettertouchtool`
* entered in Terminal `sudo rm -rf /whatever`

went to /Library/Preferences

* removed *.GlobalPreferences.plist*

went to ~/Library/Preferences 

* removed *.GlobalPreferences.plist*
* removed *com.apple.AppleMultitouchTrackpad.plist*
* removed *com.apple.driver.AppleBluetoothMultitouch.trackpad.plist*

Finally I did a PRAM reset (Reboot, immediately hold `alt/opt`+`cmd`+`P`+`R` and hold these keys until the computer restarts and you hear the startup sound for a second time]

Frankly I got this by hit & trial, I didn't knew what to do, so I did all at once. After it restarted my trackpad was back like again. Maybe someone can edit this answer to make it perfect. Thanks :)
First disable/quit BetterTouchTool. Then go to ~/Library/Preferences and rename/move/delete *com.hegenberg.BetterTouchTool.plist* and *com.apple.driver.AppleBluetoothMultitouch.trackpad.plist*. 

Since you didn't specify the version of your operating system the name of the trackpad preferences may vary. I got mine by sorting the items in the Preferences folder by modification date in list view and changing some settings of the trackpad prefs. Then quit *System Preferences*. Look for an *com.apple....* containing trackpad or HUD. Don't throw away *com.apple.systempreferences.plist*.