AM or FM?
In a nutshell....
FM - good signal to noise at a penalty of high bandwith
AM - low bandwidth at a penalty of poor signal to noise
You pays your money....
By the way, even a lousy performance narrow band FM system using 5kHz of deviation and a peak audio frequency of 3kHz still needs a bandwidth of 17.5kHz - no good for 8.33kHz spacing.