As to FM vs NFM - YMMV
All depends on how good the Radio Tech's were who installed the Narrowband system.
All depends on your Scanner. Only you will know what SOUNDS best to your ears
T-Band - Varies here in New England. Agencies were initially required to NB
then the FCC exempted them.
Some had already gone NB
Some had funded it already and continued to NB
Others still went NB as they had to touch the radios anyway due to 450-470 Mhz channels in the same Radios.
Others it varies, and only the Tech's will really know.
Again - see YMMV and experiment as there will always be exceptions