Try: 252 SpAtk, 252 Spe, 4 Def
You want 4 EVs in Defense since you have Bold nature. 252 Special Attack is to hit your opponents hard with every form, since the move it learns depending on its form will always be a Special Attack. 252 Speed is because Rotom forms have mediocre Speed stats (they're not going to wow you with speed, but 86 base speed isn't awful either). Bold nature is an ok nature, since it lowers Rotom's useless Attack and bulks it up. Remember that all Rotom forms have the same stats so its EV spread will depend on how you play it. You could even go the bulky route and do 252 HP, 128 Def, 128 SpDef. Hope this helps!!!