To add on to what TheTabKey said, Adamant also allows for a guaranteed 2HKO ahainst Unaware Clefable which Jolly only does 50% of the time. It also does much more damage to switch-ins (which are mostly defensive in nature due to Mega Medicham's attack, thus not requiring the extra speed from Jolly).What do you guys think is the better choice for Wallbreaker Mega Medicham: Adamant or Jolly?
For whatever it's worth, Adamant Thunder Punch also guarantees a 2HKO against Slowbro. Adamant also allows High Jump Kick + Ice Punch to 2HKO standard Celebi (if Jolly, you need 2 Ice Punch in a row, so you can't mindlessly spam High Jump Kick).