We've had mayo a couple of times. I find it OK for a change from the usual, I prefer butter, but most times nothing at all. The corn we had Monday was really good so I ate it straight from the grill without any seasoning or butter. MMMmmm!
It's interesting that since I started grilling corn, most of the time I don't top it with anything at all either. That's especially true of corn I grill in the husk as it's very sweet. Corn I grill with the husk off might sometimes get a little bit of butter and salt as I find it a little bit tougher.
However, if I'm at someone's house and they serve boiled corn, I almost always have to reach for the butter and seasonings.