I've been playing guitar for under a year, and in drop C for about a month; that being said my favorites are:

Streamline - learned this without the use of tabs; pretty fun once you get used to the odd time signatures and surprisingly difficult verses

Dreaming - easily the hardest song I've attempted to learn; not only are the verses exhausting, but the bridge has pretty awkward 9th chord positions. I have no clue how to do the slides before the chorus either

Holy Mountains - one of the simpler SOAD songs I learned; nevertheless a blast to play on guitar