This is ultra difficult...
S1:
- Really showed Team S' power for the first time. Cute girls, amazingly tight dancing... Love Hoshi no Ondo, Rena bouncing on Sakura no Hanabiratachi, and the rest.
S2:
- Many instant classics; Ame no Pianist, Wimbledon, Glory Days, etc... but also a lot of songs I'm not that fond of.
S3:
- Hardly has any songs I don't like. Great all around, love most of the outfits, Rena solo!!
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Based on sentimental value I'd vote S1, but I'll go with S3 for the super high all around quality.