Trying to decide on what tranny fluid to use...

[clean2g]

My tranny is coming back from Shep this week and I'm trying to decide what tranny fluid I should use in it. I just got the basic AWD rebuild and I don't plan on dragging or making lots of power anytime soon. He recommends Pennzoil Synchromesh for most cars, and I've heard other's say Red Line, and up until now I've been using Royal Purple 75W90. What are your experiences with Red Line, Pennzoil Synchromesh, and Royal Purple? I know there was a related thread about this before but all I still don't understand what the differences are between the three. (The car is a 97 GSX)