If you had to give Megas to one legendary trio, which one would it be?

I'd probably choose the Lake Trio:

>Azelf
Psychic / Fighting.

HP, DEF, and SPDEF all lowered to 60.

165 in both attacking stats, 135 base speed.

Ability: Iron Fist
New moves: Superpower, Close Combat, Mach Punch, Shadow Punch, Bullet Punch, and Swords Dance

>Uxie

Psychic / Steel

150 in both defenses, 95 HP. Both attacking stats reduced to 60. Speed unchanged.

Ability: Magic Bounce

New moves: Dark Pulse, Taunt, Will-O-Wisp

>Mesprit

Psychic / Fairy

120 Defenses and Attacking stats. 110 speed, and 115 HP.

Ability: Magic Guard.

New moves: Moonblast, Misty Terrain, Recover