>>12807145I make it a point to go through underleveled. I never grind on wild Pokemon. I do, however, beat down all the trainers and, if the game has it, equip a Lucky Egg or Exp Share. In other words, I just blaze right through the majority of the game in order to make the boss fights (i.e., syndicate and Gym leaders) actually difficult. Oftentimes I'll barely get through a first attempt at the Elite Four because I managed to chain-revive until the bastard ran out of Fire Blast or Earthquake or what-have-you, at which point my team composed of NU goodness can begin a counter-sweep.
But I digress. If you want to beat the games quickly, don't grind, keep your party to around two-four members, and USE ITEMS.