OK, I will be the long straw in the bunch.
All of this year comparison and trim comparison in this car may be nice, but it seems that everyone is price conscious period.
Price would be a factor if you were talking about basically the same product. The Leaf comes in several flavors, and everyone seems to be agreeing that the "flavor" automatically has difference "value". I say that the "flavor" is irrelevant, just like when you buy a used car, you may not get the color you wanted.
My feeling that buying a used Leaf is just like any used car, you want the newest, lowest mileage, and best battery car you can. The Leaf is unusual in that you can get a junk Leaf for $5000, and a great Leaf for about $10,000 - a $5,000 spread. Buying a used leaf is like buying a loaf of Italian bread. You want the freshest one you can find. You should spend what you can afford to get the best one you can, because for only a small amount more you are saving yourself future headaches, and preventing surprise expenses.
My top pick for a used Leaf is what a gentleman on this site recently bought (which happens to be the same car I have). He got a 2015 "S" with QC package with 12K miles and perfect battery for only $10,000... Everything you need in an electric car, with no $$$ filler options.