As for rankings…S2 was when I became absolutely enthralled, though I was watching from the start…(FB recently gave me a memories from 2012 posting on how it was almost Once time…)
I liked the Frozen arc because I loved the portrayals of the characters.
And any arc where Belle isn’t entirely asleep is a good arc as far as I’m concerned.
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Keeper of Belle's Gold magic, sand dollar, cloaks, purple FTL outfit, spell scroll, library key, copy of Romeo and Juliet, and cry-muffling pillow, Rumple's doll, overcoat, and strength, and The Timeline. My spreadsheet: https://drive.google.com/file/d/0B6r8CySCCWd9R0RUNm4xR3RhMEU/view?usp=sharing