^Just play the game however you want. EV training from the start would be too complicated and too little fun. Until you've beaten the E4, EV training shouldn't be a concern at all.
That being said, if you happen to bump into a, say, Jolly Axew or Adamant Drillbur on your travels, you should put it in a box for later and use something else in-game.
After the Elite Four, you will have access to a whole lot more stuff to effectively EV train, such as Fly, the Power Items, Exp. Share, TMs stronger 'mons to do the dirty work, etc. In short, pleasure before business. Have fun, beat the game, then EV train.
That being said, if you happen to bump into a, say, Jolly Axew or Adamant Drillbur on your travels, you should put it in a box for later and use something else in-game.
After the Elite Four, you will have access to a whole lot more stuff to effectively EV train, such as Fly, the Power Items, Exp. Share, TMs stronger 'mons to do the dirty work, etc. In short, pleasure before business. Have fun, beat the game, then EV train.