I have one hole-in-one in my life and it was on a short Par 4 - 324 yards.
Pretty straight hole with a slight down hill about 75 yards before the hole, so when you're standing on the tee box, you see fairway and then the crest of the hill and fairway concave down, and then the green.
I hit a baby draw with the driver and never saw it land as it landed on the backside of the little hill in the fairway, and I stood on the tee-box waiting to see if I drove the green because 324yds downhill is a quite achievable drive, and then all of a sudden here comes the ball rolling up on the green and it just casually rolls into the hole. It was like the perfect shot, because it slowly rolled into the hole - almost stopped short.
I've been extremely close to several other aces, but that's my only one. Had a few par 3's hit the pin, and a few lip out. Had one almost dunk in on the fly and it left a pitch mark on the edge of the hole - pretty much destroyed the hole and somehow didn't go in.