What do you guys think is the better choice for Wallbreaker Mega Medicham: Adamant or Jolly?
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).
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).