
So I ordered a few capes recently from Whiting Farms, the leading breeder of genetic hackles. Although they are known for the superior hackles for dry flies, Whiting has broadened their product line with any kind of feather imaginable, from feathers for streamers, spey flies to bass bugs.
The most popular line of hackles are the capes and saddles for dry flies from the Whiting line, also known as the red label. This red label capes and saddles are basically from the birds Whiting bought from Henry Hoffman. The other, of a more historical importance are the capes and saddles from the Hebert Miner (green label) line. The current birds have evolved from the very first roosters specifically raised for dry fly quality hackles by Harry Darbee. Here's a very nice overview of the history of hackles.

About the improvements of the hackles:
Most of my capes and saddles are from the late 1990 and early 2000 era. The most recent one I bought was a Bronze rated Whiting cape (darker barred ginger) I bought in 2006. It's now almost 10 years later and the improvement in quality is quite remarkable. From what I read and heard, every generation seems to be an improvement over the previous generation of birds.

The highest rated (Golden or even Platinum) capes or saddles (which has an even narrower size range than capes) with predominantly hackles in the size 18 and smaller (as wonderful as they are!) is simply not very useful for general use. It's an odd thing to say but Whiting has improved their hackles too much! So, where does this end?...
Update Nov 25, 2015:
Here is a nice article about the history of hackles from Field & Stream (March 1985):