Puppy 4.31 is the most common version of Puppy 4. It works well on a wide range of computer and may perform better than Puppy 5 if you don't have a brand new computer.

Puppy 4.3.1 release announcement on Barry's blog
Puppy 4.3.1 release announcement on Puppylinux.com

Puppy 4.3.1. superseded Puppy430.
There is an enhanced version called Puppy432.
Barebones431

Discussion on the advantages of 4.31
Simplified Puppy 4.3.1/4.3.2 Upgrade Center