A: Psychic B: Luster Purge
DON'T POST YOUR OPINION FOR ANY OTHER MOVES. A-OR-B
Latios generally prefers Psychic (or Psyshock). Luster Purge might have an awesome secondary effect but it just isn't worth it. The foe is just able to switch out from the Special Defense drop. The low PP and base power of 70 leaves it as a less than ideal move to use.