If there's one model I wouldn't go for used, its the 2016. I purchased a brand new high spec 2016 model recently from B&H - having it less than 60 days, the Logic Board (as well as hard drive graphics card etc) and the screen were replaced all because of a minor graphics issue.
If it wasn't brand new (or had Applecare after the first year) I'm sure the repair would have been costly. Being that these machines are notorious for having graphic and keyboard issues, I'd stay away from them as a potential repair cost could wind up setting you back for the cost of a new one (in total)