I have been lucky to have three aces, with one in competition. I have also seen two others, one as a caddy in the Women's U.S. Open in 1983.
The second ace I witnessed was unique. You have all read about the ace that goes in the hole after hitting a trash can/tree/ball washer/golf cart, etc, etc.
I was playing in a charity event offering a BMW roadster for a hole-in-one on #9, a 170 yard nothing-special par 3. As a consolation if there was no ace, the closest-to-the-pin was a set of new Hogan Apex irons.
I was in on of the final groups to play the hole, and as we looked at the green when we stepped on the tee, the "closest to the pin" flag was about 3 feet away. I hit first and got lucky and hit it to 6 inches, with all the witnesses jumping and screaming as the ball almost went in the hole. Although not driving away in the Beemer, I thought I had won the Hogans for sure.
The guy behind me then steps up and hits a screaming low heel pull that rattled around in some trees left of the green (uphill side of the green). The trees spit the ball out, it rolls toward the hole, and you guessed it, it goes in for an ace and he wins the car. I didn't win the clubs because there was an ace - ouch. Boy was he excited to relinquish his amateur status to get that car.
The punchline: the amazing thing about his ace was that his ball caromed into the hole off of my ball which was sitting 6 inches away. The officials at the green had measured my ball at 6", and after he used it for a backstop, it was 4' away from the hole! That must have been a fairly hard "carom". He used not only the trees and the downhill slope from the trees, but also my ball - all to get his first ace, and no doubt his first BMW roadster, too.
I did not win the clubs but I did get a great story.