Harrinton on Holdem 1 and 2 are my picks.Both combine to form 1 large book.There is enough math in these to play poker well.More importantly there is plenty of the other info needed to play.
These books are a must read for any tourney player,but have plenty of info that applies to cash games as well.
As far a Sklansky goes I have never read any of his books.I do know he is the math wizard of poker though.Couldn't go wrong with his books either.