It's difficult to evaluate them since they all serve different purposes. I Will Remember You was heartbreaking, but it manages to convey so much about the Bangel relationship. It's tantalising, much like B/A in general "“ they're constantly struggling against their own limitations, the circumstances that force them apart. It's ironic that when they're together, Buffy and Angel fall in with each other effortlessly, no matter when or where, because they're always under the strain of the wall that separates them, trying so hard to hold on to each other. By giving them a moment where they have that sense of freedom to love each other, IWRY encompasses both the ecstasy and the tragedy of B/A, and I suppose that's why non-B/A people tend to find it superfluous.
I actually liked Sanctuary/The Yoko Factor simply because it revealed a lot of Buffy's anger at Angel and allowed the two of them to move past the demons left over from S3. It was necessary, and seeing Angel in The Yoko Factor reminded me just how much I missed his interactions with Buffy in BtVS.
Forever was classic, obviously. Buffy's "How about forever? Does forever work for you?" is among my favourite lines in the series simply because it's so hopeless yet so sincere. It's just so beautiful to see them nestle into comfortable silence together, Buffy knowing that he's there for her in her darkest hour, and that being enough for her to make it through the night.
As for End of Days/Chosen, I very much enjoyed their meeting "“ it was a confirmation (at least to me) that the two of them would have a future. Undoubtedly, her final words to Angel could be interpreted as something that she would have said to any of her past love interests, a declaration that although she wasn't looking for a serious relationship with them anymore, she could see one in her future, but that reading isn't consistent with my understanding of Buffy as a character. It makes her sound manipulative - like she's thinking, "Gee, I'm not sure who I'm going to end up with, but this guy's still pretty hunky, so I'd better balance the stick with some carrot, keep my options open." I can't see her calling Angel back, after explaining that she's taking a break from serious relationships until she knows more about herself, in order to tell him that she can see a future with him, for any other reason than to reaffirm their lifetime bond. It mirrors the scene in Bad Eggs, as Kean pointed out, and there's no way Angel doesn't know that as he exits into the shadows. I can't see Buffy throwing him a bone that big unless there was real meaning there, a real promise from her that the two of them have a future, and from him that he'll wait forever for that day.
Overall, I guess they're all my favourite in the sense that they each fulfil their purposes perfectly. IWRY was almost like a tribute to the Bangel relationship of S1-3 and all that it stood for, Sanctuary/The Yoko Factor let them deal with the aftermath of their break-up and move past it, Forever showed just how important they still were to each other and Chosen made the promise that their story wasn't over. That about sums it up for me.
