Several good answers already given. All things being more or less equal, discuss all dates in the bibliography or notes, and pros/cons on each. Myself, I would go with bible records, usually the closest to the event, although sometimes changed from family pride and such, or just spite. Had a great great grandmother whose name and dates were scratched out of the bible because her children didn't like her very much; scratched out so hard they wore a hole in the page.
I've found several incorrect gravestone dates in my family. The carver messed up on one and my grandmother could't afford a new stone; watch out for replacement stones too, my great grandfathers stone was replaced about 50 years ago and they got dates wrong.
Another cause is not uncommon in low income or poorer areas and counties; stones were not placed for several years and the carved death dates will be years after the actual demise. More common in the 1930s.