It really depends on the trailer. Most trailers play the orchestral version of One-Winged Angel, the one in FFVII Reunion album. There are a few trailers that play Advent: One-Winged Angel from FFVII AC's soundtrack, though. Two fast ways to distinguish them:

1) OWA (Reunion) has only orchestral parts, AOWA (AC) has the Black Mages playing.
2) Their lyrics are different. OWA uses the traditional lyrics used in FFVII, KH and many other places, AOWA has totally new lyrics.