I put just as much thought usually as to my bag setup on a trip as I do to the actual contents of the bag. It's all about having what I need and being able to maneuver properly in all the environments from trip start to trip end.

For frequent travelers on repeat trips, bag setup is easier because you'll know 85-100% of the following each time [trips are rarely 100% identical each time]:
* exactly what you need to carry for length of stay
* both departure and arrival airport difficulty level, lines, including security, distance between security and departure gates or arrival gates and immigration/exit
* Airplane type[s]/Size/compartment restrictions [also your status level for boarding priority; last people boarding are more subject to gate checked]
* ground transportation process-taxi-shuttle-rental, walking, rick shaw, etc
* accommodation setup-Hotel[s] type.
* Limbo time [transition or waiting time spent somewhere you'd rather not be]
* and all the peculiarities of travel

On those trips where everything is "perfect" or I know for whatever reason, good or bad, that I'll be spending much time in the airport, I'll take a roller.
But on the majority of my trips, especially in Europe, I take a Timbuk2 Wingman or other carry on 'duffle' bag and sometimes a second smaller bag because they are the most versatile.

I also find it easier to keep my duffel in my possession, in almost all circumstances. Service workers seem to be always more insistent on separating you from your roller than a duffel in almost every circumstance.

As has been mentioned, It's better to have different bags for different trips.