Writing the UIG book forces you to nail down exactly what the roles of the various Elites is. Rangers and Marshals had a certain degree of crossover before as they both operated as solo law enforcers. The role of each has now been clarified and they should be really fun to play.
Rangers - They are specialists in ranged weapon and traditionally operate on their own although this is obviously not true of Black Squad rangers as they need to work in a team. A ranger's primary function is to track down a target and either gather intel on them or eliminate them. You could thus think of them as slightly James Bond-like, travelling the world, sneaking about and if necessary, dispatching a few key kingpins.
Marshals, on the other hand, are masters of the modern city. Their main skills lie in the ability to understand the machinations, crime and structure of a new city in an incredibly short time. This unsurpassed ability to gather intelligence allows them to add anyone they have a conversation with as a one point contact. The idea behind this being that (much like Sherlock Holmes), they need simply cast their eyes over them to understand the way a person ticks - this gives them the leverage they need force them into compliance. Each subsequent meeting adds another contact point as the Marshal gathers more and more information about the subject.