Um, no? Jolly Mega Heracross has 273 speed, Jolly base Heracross has 295, Modest Mega Gard and Adamant Char-X has 299.They can run both, Jolly is useful for outspeeding neutral natured base 100s, while Adamant is for better wallbreaking.
Jolly is better as it forces Mew, Gliscor, and other checks to speed creep you more taking away from other possible investment elsewhere.Do Mega Heracross run Adamant or Jolly? Should I run Jolly just to outspeed D-nite and Altaria, but they both run Adamant/Modest anyway...