Each `lecture` is comprised of recommended reading material (sourced from LYAH, RWH, Typeclassopedia, and others) and some reasonably difficult homework problems that build on the learned concepts.
They're likely both good starting points. From a cursory glance of Spring 2015, here's why I like 2013 more:
2013 starts with Functor and builds into Applicative then Monad. I like this a lot, as each builds on each other: fmap has a tight relationship with <$>, and Monad is pretty much Applicative with bind (>>=). Applicative is a Functor and Monad is an Applicative (as of 7.10 I think).
I'm by no means super experienced here, but the 2013 course was the first learning text that really got me into Haskell.
Each `lecture` is comprised of recommended reading material (sourced from LYAH, RWH, Typeclassopedia, and others) and some reasonably difficult homework problems that build on the learned concepts.