If you go by the number of the particular Inspector series that will be made available, I would go with the Nettleton first as there will only be 4,000 made, and they should be over 48,000 by now as mine was in the high 47,800 range and received in November 2005. The Custer gun is also worth getting, but I would go for it as the second choice since some 14,000 Ainsworth guns will be made. My Custer gun was in the high 6,000 range and received in January 2006. My intentions are to also order a Clark and Carr gun, making the Clark a 5 1/2", and leaving the Carr as regular. This way my Inspector series collection will have some variety. If your are able, go for both now as you can't go wrong owning USFA's.
As a side note to Rawhide Rio, the Custer gun is not marked in any way to infer Custer himself. It is a nice Ainsworth gun in the Antique Patina finish, and does look period correct in many ways.
Either way, you will be happy!