dont think there's any real diff except for the 5 speed and 6 speed...i thought maybe it could be the number of valves..but from what i've seen they're both 20v...i guess the GLI coes with more options than the GLS...and has better reputation and recognition...i havent seen any GLS jetta's with a badge on them so if anything just get a GLI badge and slap it on lol..