It's a whole lot easier to raise happiness than it is to lower happiness. In fact it's easy to accidentally raise happiness without trying.
One exception: Revival Herbs. It is a max revive, but it is bitter so it lowers happiness. So after all EVs have been gained, E4 training gets difficult to do quickly (without Exp. Share or switch out training) so using Revival Herbs a lot may want to alter your choice. Then again, you can just go to Gear Station and put a heavy object on B and down so you run for hours on end... that's how I do it.