Really depends on your primary use of PhonyShop, yes?
If it's not learning the program, but learning techniques, then the Kelby book. His techniques are first rate, but as an author Kelby does not resonate with those who do not like his flippant 60s hippy dippy writing.
An alternative is How to Wow PS for Photography (2nd CS2 ed) by Davis & Willmore. Very fast strong techniques. There are two techniqes in this book that sometimes make me more money per workday than cost of the book.
If it's working with RAW, and learning to get 90% of work done in RAW, so all you have to do is sharpen in PSCS2, then certainly Bruce Fraser's CS2 RAW book. In fact, if you relate to his writing style, anything by B. Fraser on RAW, Sharpening, color management, PhotoShop, scanning, Workflow, etc., will save time and money.
He be 'da Man.
E.g., shot this today on Manual @ "Sunny 16."
http://postit.rutgers.edu …ron%5FSledding%5F12%2Ejpg
All work in PSCS2 ACR RAW converter, NOTHING in PhotoShop other than a light capture sharpen, as per Fraser's recommendations (his PhotoKit Sharpener). The tonal range and quality stun me. I relish high contrast photography.
Jack