The Gift is amazing within the context of the S5, but as an individual episode in itself I don't think it's anything special. If I were to watch the episode just by itself without any knowledge of the pain and hardship Buffy had gone through in S5 (The Body - losing Joyce, Dawn, Buffy's catatonic trauma - Weight of the World, Glory etc) her speech at the end about "live, for me" just wouldn't have as much impact as if I were to watch the episode as a stand-alone.
Becoming is completely different - I think that episode got me properly hooked on Buffy. A casual viewer can watch this episode and get so much out of it.. So I'd go with Becoming (both parts) as my favourite, followed by Graduation Day (Part 1 is better - the Buffy/Faith fight is epic!), followed by Restless, then The Gift, Grave, Prophecy Girl, with Chosen last. Which is a shame, but after a poor S7, the episode just doesn't really do much for me these days.