I've read both, and I certainly don't regret it. The financial sector is not my area of expertise, but I feel much better informed after reading these books. They give a good background on both the entangled government-financial sector freak out to avoid total collapse (Sorkin) and the small set of contrarians who were able to see each domino being lined up and place their bets before the first one was tipped (Lewis) -- while expressing their utter amazement at how messed up the system was.

Now, if you're looking for an easier read, go with Lewis. I'm going to have to read Sorkin's book again before I can really say I entirely understand it. There are a lot of names, a lot of connections, and a lot of concurrent actions that are hard for an outsider to fully grasp. Sorkin doesn't it masterfully, but there's only so much he could do with such a complex story.

As a side note, I haven't read the Lowenstein book mentioned by Steve deHaan, but being very familiar with Lowenstein's research, I bet it's worth a read. In fact, if you're looking for something that's less of a story told by a certain cast of characters and more of an analysis of the human, psychological factors that led to the collapse, Lowenstein's probably your guy.