(My train broke down before I could leave so I can answer one more question)
I understand why everyone is choosing Bad Apple!!, Necrofantasia, Hartmann's Youkai Girl (actually I don't understand this one, everyone seems to hate it just because Lost Remote is so much better), and so forth. I really really want to give this to U.N.Owen, because it's also overrated...
But I'm going to go with Bloom Nobly, Cherry Blossoms of Sumizome ~ Border of Life. If the ten billion remixes of this indicate anything, it's that everyone likes this song. There was a time where every Touhou arrange CD had an obligatory remix of it. Yuyuko could set up a massive sound system in Hakugyokurou programmed to play nothing but Border of Life remixes; she won't run out for several months.
Note that I actually really like Border of Life. Overrated ≠ bad.
PS: Janitors, keep an eye on this thread, it's almost to 1000 posts.