OK, by popular demand I was asked to rank the best defensive teams of all time. The Kansas City Royals ranked No. 1 on Buster Olney's list for 2016 and it's certainly possible that the 2014 or 2015 Royals would rank high on any all-time list.
The problem with historic evaluations of defense is that we don't have the same precise measurements as when looking at offense. The Defensive Runs Saved era goes back only to 2003. Before that, Baseball-Reference uses the Total Zone system to estimate runs saved on defense. So we'll use Total Zone and consider general reputation as well.