Well... Might I suggest a Ralts or its evolutions?
Ralts@ Any Item
Calm, Gentle, Sassy, or Careful
Grass Knot and Confusion grab an easy 4 hearts apiece. Psychic is for if you do poorly, or if you simply get first somehow. Calm Mind is support. The natures make sure it can get the most boosts from the bitter berries. Found on Routes 208 and 209.