If movies are being considered you'd then have to say that Nemesis was really TNG's finale since that was their last one and they all go their separate ways. But I don't think many TNG fans will buy that one.
Really, both AGT and Nemesis should be considered as finales for TNG. A finale has evolved as a genre of presentation; it is not simply the last of something. All Good Things is clearly the finale as a series. Nemesis is the finale as a a film franchise, although I think there was some ambivalence about actually designating this as the end.