The only problem with using factory radio speakers, in the doors or rear deck, is they are wide range music speakers, AKA Hi Fi. Not what we would want for two way radio audio.
If you look at the speaker cone in a Motorola, Kenwood, Icom, or other two way radio speaker, they are harder so the frequency response is in and restricted the 300 to 3000 Hz voice range.
So, it comes down to personal choice.
The father of Police Radio on the west coast, Herschel Calvert, gave me a Motorola T Power speaker back in the late '60s, and that is still the best sounding speaker for two way.
LAPD in the 70's changed out the speaker in the rear deck to the same speaker used in the Motrac.