With the re-release of FF6, which I haven't played in full for at least 10 years, I can truly say it is the epitome of the main Final Fantasies.  Hands down... there IS no question here.  The gameplay is tight, the graphics for its time, and even now on the GBA, are crisp and I will take this cast over any and all Final Fantasy casts.  Because you care about all the characters.  There is no emo character here, no anti-hero that we all love to hate.  Heck, the (arguably) two main male and female leads, Locke and Terra, aren't even romantically involved or doing the whole teenage fawning crap we see in FF following this one.  And the music?  Fuggedaboudit....  the best.  Only a handful of Uematsu-san's other works can even compare.

I've enjoyed most of the FF games, with the exception of FFVIII.  FFVI is the opposite of everything FFVIII stood for or implemented.  The little sprites of Terra, Edgar and Celes are all much more fully realized than the CGI/90210 SeeD school kids.

OK, enough ranting... going to finish work so I can go home and enjoy the masterpiece.