Which Kadee is best?

I am in the process of changing the couplers on my “old” locos. I have a mix of Athearn and Atlas(Roco and Kato). I had some information on which coupler was to be use on a certain model like an Athearn GP38( #37 or 38) but a #5 did a faster and job. Is there a chart somewhere? Keep in mind that my locos are from the 70’s and the newer are from 4-5 years back.

Thanks for the help

Check here first:
http://www.kadee.com/conv/list.htm
There’s a nice discussion about this sort of thing here:
http://www.trains.com/community/forum/topic.asp?TOPIC_ID=30369