I love Biyuden. It's my favourite group in H!P and I can say it actually got me into it. As for favourite songs, I haven't heard any b-sides yet as the server is quite whacky, but my favourite of all time has to be Aijisai AI Ai Monogatari. And the PV dance is so corny that I like it. Aisucream to My Purin's dance is great too. I know it by heart.
I'll watch the concert later. I look forward for the Pajama na Jikan performance. I actually like that track. <_<