I think they're both excellent. Manhattan has some useful insights about how to approach questions and the lines of thinking that test-takers should try to emulate. The comments on "How a 170+ tester might think" are the highlights. But useful as they are in their own right, Manhattan books can't touch PS in LR and LG, for which the Bibles are the gold standard.
I think someone who is strong in RC and only needs help for LR and LG can focus on the Bibles and do great, but anyone with room to improve in RC could probably benefit from Manhattan.
I'm not a Manhattan employee by the way. I know it's kind of suspect given my low post count, but I have pretty extensive posts in the June Prep thread that would be very unusual for a Manhattan employee. I also don't think Manhattan books are perfect--I'm very annoyed by a typo in the answer key in the Atlas 2009 LR book, which led me to think one of my answers was wrong when it was correct, and forced me to try to justify the "correct" answer (i.e. the wrong answer that I was led to believe was correct by the typo) that ultimately proved to be an exercise in reinforcing bad reasoning.
Do take my words with a grain of salt because I don't have any real LSAT scores (only PTs) to show for the purported benefits, and even I can't accurately gauge how much of my recent improvements is attributable to one set of books and how much is attributable to another. I also used the 2009 books, not 2010.
Manhattan folks, if you believe the 2010 books are not only typo-free but substantially better (as many publishers claim, though not convincingly, about new editions of their books) than the 2009 ones, I'd be happy to review your 2010 books. Just send 'em to me free of charge and I'll post a detailed review here.