i would say the modular pulley. easy to get off and put the 3.8 on. is your pcm tuned for the 3.5 pulley??
ive never taken a pulley off so i dont know how hard it is to get it off and put it back on..
(i wrote this a while ago but my mom came in and said gas was going up by the hour and its 5$ a gallon so i jetted off)