Which nature is preferred for a Mega Gardevoir?

Question

Modest or Timid? Stallers are very common but Gardevoir has enough Sp.atk already. Which one?

Answer 1

Depends on its role.

Either Timid or Modest would work for for a straight up sweeper with all attacking moves, for more power use use Modest, for more speed use Timid.
But if you want a Will-O-Wisp and Taunt stallbreaking set, always go for Timid.