2nd one- they are both the same but the 1st is a lightweight version; I tend not to trust light weight versions of drivetrain parts..
You will also need this to match it though:
http://www3.towerhobbies.com/cgi-bin...?&I=LXJBM3&P=M good
The buggy version ( 43/13 ) has straight cut teeth like this:
http://www3.towerhobbies.com/cgi-bin...&I=LXLGU1&P=SM bad
And wont mesh with the spiral cut truggy gears ( 43/10 ).