For what it's worth, TC was my favourite track from ATS and BID is in the top 3 for LT.
I'm sure every first single selection has it's own reason. TC obviously for being the theme and the climax of the album, while BID had the most 'energy' (as the band phrases it) of the album.
In a way, I think the first single selections also kind of represent what the album is going to sound like.
OSC/HT -> Heavy
SIB/Meteora -> Heavy but more angsty/emo
WID/MTM -> Softer
TC/ATS -> Electronic, creative, different song structures
BID/LT -> Electronic, catchy, shorter 'firecracker' type
Just my two cents.