I have only read Eric Evans' book, but it is excellent and still very relevant.
Yes I would definitely recommend Eric's book for the deep insights it contains, but it may not be the easiest to read, especially for non-native english readers as his english is quite formal.
Scott Millet's book is also very good.
For an introduction to DDD you can have a look at a conference video here my friend Thomas Pierrain and I made : http://videos.ncrafts.io/video/167722768 (shameless plug :-))
I personally found the Vernon book to be overly repetitive and actually light on real application guidance. It almost turned me off to DDD.
The Evans book is the better investment by far.
While Millett and Tune's book is generally good, it too is very repetitive about the fundamentals.
Vernon's Implementing DDD is an excellent supplementary book to Eric Evans', but it also works well as a Stand-alone book. I generally refer to them as "the Blue Book" (Evans) and "the Red Book" (Vernon). I still haven't read the Blue Book, but I will in due course. The Red Book has given me more than enough understanding of DDD to put it into practice in the workplace.