These days the main thing is making sure you have a full group, what ever zone/camp your at so long as you are in a sweet spot if xp per kill / kills over long period will end up better then focussing on specific bonuses.
It's half the reason some hotzones suck, they are too 'difficult' and too little exp per kill to make up the bonus vs lost kills somewhere else. Or the zone themselves just don't afford any ideal camps to keep kill rates up to make exp worth it.
It's like, older higher level content is generally better exp than newer higher exp harder content. Especially in level relevant expansion cycles with a difficulty increase.