I taught both my Smeargles these moves, hope this helps other people:
- Acid Armor
- Dragon Rage
- Leech Seed
Smeargle will learn the move Sketch every 10 levels, you can copy any move permanently by sketching the pokemon you battle. If you are in a hurry, take it to the move tutor, he will learn sketch immediately, as long as he doesn't still have sketch in his moves already. Search throughout the game until you find enemies with pokemon with the best moves. It is convenient to use VS Seeker to battle your opponents again in case you miss the move.