Best version of Hadoop for Nutch 2.3.1

[Michael Coffey]

What is the best version of Hadoop to use with Nutch 2.3.1? I see that the 
runtime/local/lib contains .jar files for hadoop 2.5.2. Does that mean I should 
use 2.5.2, or would a newer version like 2.6.5 be even better?