Well, here's what the rules say:
(a) The occupied bandwidth of emissions transmitted on the center frequencies 151.820 MHz, 151.880 MHz, and 151.940 MHz must not exceed 11.25 kHz.
(b) The occupied bandwidth of emissions transmitted on the center frequencies 154.570 MHz and 154.600 MHz must not exceed 20.0 kHz.
Your radio should keep you inside those limits, as in it should not let you select 20KHz for the 151MHz frequencies.
For the 154MHz frequencies, you can run either one. The wider bandwidth may give you a bit better audio and a bit more range.
But, you should be running what ever the other radios you are talking to are running. Running the wrong deviation will result in distorted or quiet audio.