In this guide, I will present to you the utility of Vital Spirit(Ability) in exp farming.
Vital Spirit(Ability) - outside of battle effect:
Attracts higher level enemies.
This means that, on average, we will be encountering mons with greater levels, which should increase the average exp gained.
How much? It depends on the spot!
Example
General formula for exp increase:
5*(Amax-Amin)/(2n),
where Amax is maximum exp gained at given spot,
Amin is minimum exp gained at given spot from killing a single mon,
n is range size
(no mixed species spots)
Proof(simplified)
Example
The difference might not seem to be significant, but using a Vital Spirit mon should increase your experience gain in the long run, so it's worth considering.
Especially when using exp bonuses.
Mons with Vital Spirit ability:
as Hidden Ability:
Out of these Primeape, Vigoroth, Electrivire and Magmortar seem to be the best options for efficient exp farming
as they can learn strong multi-target moves like Earthquake or Rock Slide,
and have good overall stats.