Aftermarket Wiring Harnesses

So I have been reading a bunch of posts about wiring harnesses. It seems that a favorite are Ron Francis and American Autowire. There are also a bunch more out there such as Painless and Ezwire etc..

Myself I have used a Painless harness and I thought it was very well made and worked great. The instructions where vague in a couple areas, but with a simple phone call I figured out where that wire was to be terminated. Im currently looking at a EZwire 21 circuit to rewire my Scamp.

So with a whole array of different harnesses all with different prices. Most of which look to be very similar. What makes one better than the other?