Your question is baffling. The fact that you specifically said "EV train" means that you know something of the sort exists already in the game. And EV training is ridiculously easy once you understand the mechanics of it. As for obvious, no, not necessarily. Take Cranidos for example. Its attack is high yet special attack is crap so giving it attack IVs make sense. It's a rock type so you figure its defenses are good, right? Except Cranidos is as frail as an old statue. Tip it over, and there's no fixing it. Defensive EVs, pointless unless you have a plan brewing in your head.