A17 is WAAAY harder overall, it really forces you to work as a group on MP, we are currently back on Navezgane as the RWG is currently a bit buggy (radiation zones in random places, holes in the ground etc)
We already had to start over once heh, I had set it on 'warrior' difficulty with 16 Z's per person, there were just 3 of us and we got annihilated!!! the 7th day :/
Now we are at day 18 on standard settings with Navezgane, runs lovely on my server with the Z's up to 80 (Linux dedi, 7700k, 32gb, raid ssd)
The shared Xp for team members is great!