I voted for "Epitaph Two: Return" primarily because it's the one what I have seen, obviously, for the first time the most recently, and also because, with its first half, it makes a nice movie length finale to the series. In addition to that, I can see enough similarities between it and "Chosen," that when Echo has her rant about Paul after he is killed, I have no trouble whatsoever superimposing Sarah in Eliza's place voicing her regrets about not being able to tell Spike about her true feelings until it's too late. Whether you're a Spuffy supporter and believed that Buffy was IN LOVE with Spike, or whether you're something else and just believe that he was her best friend during that last season, I think that a scene like that would have been an appropriate ending for the season. Even though her actions in a dozen scenes confirmed her feelings for him, Buffy never actually said the words, not until it was too late, and she really should have. I believe that Spike earned it, Buffy felt it, and I always felt a bit cheated that we never saw it. (And I would love, someday, to ask Joss if he ever thought about that when he wrote the scene) We had a "Goodbye" scene for Angel, a "Goodbye" scene for Riley, but never a real "Goodbye" scene for Spike.
I actually, honestly, did not intend to turn this into a Spuffy rant, and I really don't think that I have, but I do believe that that one scene nailed the series ending perfectly for me, and it would have worked equally well at the end of the Buffy series. I've always been a sucker for a scene like that. So, shoot me, berate me, or roll your eyes at me. That's my favorite finale, and those are my reasons.