I'm going to post here late because I can.
I have so many favorite songs, and the list changes constantly, but I voted for Tonari Ni... because that song is BEAUTIFUL, and EVERYONE sings it well.
Even the twins.
But I also like relations, Meisou Mind, Watashi wa Idol, I Want, Massugu, and Omoide wo Arigatou. my song is great too. Also, every time it turns 9:02 pm, I start singing that song. XD
Me Ga Au Toki is also one of my favorites, and Little Match girl is beautiful. Honestly, Makoto's is my favorite. It's just so...pretty. Also Marionette no Kokoro, which is gorgeous. Miki's is among my favorites. And, last but not least...KYUN! VAMPIRE GIRL! I swear, everyone is perfect in that song. And it makes Makoto sound sexy. Just saying.
I think the first song I ever heard from iM@S was Ai Like Hamburger, so that one has a special place in my heart too.