I voted that I can't pick. So, me and RJ shall stand as one! :p
Honestly, having almost finished my 2nd time through, I love and hate certain parts of each book. I think King outdid himself with DotT and the first half of The Waste Lands. But, alas, that's 2 books.
W&G is a great story and I love the young ka-tet, but it's not my fave. I'd be split between Gunslinger, DotT, SoS, and The Dark Tower.
That's today's menu. Check back again tomorrow.