Choicing crystal or external oscillator for time critical project on PIC18F
You are interested in the relative error and/or stability, which is unaffected by any division. So, other things being equal, take the lowest ppm clock source for the best accuracy.

If 50 ppm is enough for you, I would choose the crystal for board space and price.

For better accuracy you could consider a better quality (tuned) crystal oscillator. Same physical format as a regular oscillator (14-pin DIP size), but higher price (~ $20).