Quote Originally Posted by Psychotic
Of the recurring songs, I prefer "Final Fantasy" myself.

EDIT: Ah, never mind. Same song, I got it confused with another one. Yeah, this song is definitely his best.
Yeah, Prologue and Final Fantasy are the same song. That song has been called so many things during the FFs, here's a list of (most of) them:

FFI - Opening Theme
FFII - N/A
FFIII - Opening Theme
FFIV - Prologue (also plays in the song Epilogue)
FFV - Final Fantasy
FFVI - Ending Theme
FFVII - Staff Roll
FFVIII - Ending Theme
FFIX - Final Fantasy (plays after Melodies of Life)
FFX - N/A
FFX-2 - N/A
FFXI - N/A
FFVII AC - End Credits
FFXII - Final Fantasy
FF Concert 2002 - Final Fantasy
FF More Friends Concert - Final Fantasy

I think it's a very beautiful song and a great, suitable main theme to the series, although I think Uematsu has done better songs too, such as One-Winged Angel or Melodies of Life. However, it's quite hard to beat the medley song "Melodies of Life ~ Final Fantasy" in FFIX OST (the Japanese version) and FFIX: Uematsu's Best Selection (the English version). Melodies of Life + Final Fantasy = FTW.