I have many many loco's.
How do I determine which mobile decoder to select for each one?
First, modelers with many locomotives often become bewildered at the prospect of converting all of their locomotives to DCC.
Take it one step at a time.
Consider that you are not operating all of those locomotives at the same time; start by gradually converting your locomotives, beginning with your favorites.
Digitrax maintains a list of suggested decoders for specific locomotives on our website. The Digitrax Decoder Selector can be found here:
http://www.digitrax.com/products/engine-matrix/decoder
Just because your particular locomotive is not listed does not mean that it cannot be converted.
You may find that another manufacturer makes a decoder which is specifically designed for your locomotive; DCC means that you can use that decoder in a Digitrax environment.
Otherwise, you will likely have to hard-wire in an appropriate decoder.
In this case, determining stall current is important.
In some cases, older locomotives cannot be converted; this is especially true with older brass locomotives.
Remember also that converting a poorly performing DC locomotive to DCC will not make it run any better.
You may also find installation instructions for specific locomotives on this site.