Question

I got 2 options:
1. 252 spat, 252 spdef (I think that this isn't very good because your immediatly dead if the foe use crunch or something and it has higher speed)
2. 252 spat, 252 speed.
What is the best that I can choose?

Answer 1

252 Sp Attack 252 Speed, That is the best for Gardevoir. Gardevoir is mainly used as a sweeper so you want to strike hard and Be first to strike. Evs in Sp Defence is not good at all because of its poor HP stat. The moveset you give it must have moves with Sp Attack influenced in it. Ill give you a moveset for it:

Psychic-STAB

Focus Blast-Dark type coverage

T-Bolt-Coverage

Will-O-Wisp-Burn the foe and lower its Attack

So this Moveset will be usefull because of Gardevoirs high Sp Attack.