I don't care what people say whether its a outcclassed by its regular form but Mega Scizor is probably my favorite Mega to use in competitive. Mega Scizor has been the focal point of some of my most successful teams imo from single battling and in VGC. Of course the power difference is notable but it has the bulky to setup Sword Dances and potentially sweep weaken teams with Bullet Punch, Knock Off, Bug Bite, U-turn, or Superpower.
Aesthetically I really like how Mega Charizard X turned out to be since Charizard get its black shiny skin and gets a blue flames from its tail and mouth. You can tell Ken Sugimori or whoever designed Mega Charizard X wanted to make it more muscular and physically menacing to make it correspond with the actual in-game/competitive use. I'm glad that they kept X hidden from the public until the release of Pokemon Origins just to build onto the upcoming games (not to mention an excellent marketing from TPCi).