Joy of Clojure is about understanding the philosophy of Clojure, and using the language's built-in abstractions in an idiomatic way. It's not really a "first book on Clojure" for someone that doesn't know the language at all, but if you know the basics you can use it to solidify your understanding.

Clojure in Action is more of a practical, get-shit-done book. It covers things like databases, web frameworks, TDD and message queues in the context of Clojure. It also has a brief introduction to the language itself and some coverage of functional programming idioms, but the focus is more strongly on real-world usage rather than deep understanding.