That's very hard to say. I've had so many great ones. But one that "cums" to mind is... I had been traveling for work and just generally very busy and I realized that I hadn't gotten off in more than a month. So I texted a guy I knew who like sucking cock. He'd done me a few times before and I knew he was really good at it.
So he comes over the next day and starts sucking it. Right when I get hard he switches it up and starts sucking my shaved ballsack. His left hand was holding my boner straight up and down and his thumb was idly massaging my frenulum.
Suddenly I realized I was about to cum–way too early. "I'm gonna cum!" I say. He backs off and...I don't cum. We carry on with our oral cock worshipping session and I think I said "I'm gonna cum" like five more times during it. Every time I said it I felt sure I was going to...but I didn't. Not until the last time and I blew an explosive load of hot seed into his mouth.
Very intense.