A loud, booming HA HA HA might even scare little kids! It strikes me as oddly reminiscent of an evil laugh. If the idea of some fat old guy breaking into your home at night isn't scary enough, that laugh should definitely do it. I can just see the mall photos now: Santa's face frozen in a bout of maniacal laughter while a terrified toddler, red-faced and panic-stricken, struggles toward Mommy with tears in his eyes.
Ho ho ho, on the other hand, has a good-natured ring to it. Then Santa's not scary; just a lovable old friend who brings children their presents.