I've met both, Niven, twice, briefly. He was a grand story teller, but not really approachable.

Pournelle was always pleasant.

I had the opportunity to share a dinner with JP. I was on BIX, Byte Information Exchange, their "BBS" or "CompuServe"-ish service. And Jerry would occasionally sponsor small get togethers.

So there was about 8 of us just sharing dinner at a Chinese place in the Valley. It was a great time. The man can talk, to be sure. Sat right next to him.

Unlike Pournelle, Niven is still alive (87 year old), but I don't think he is writing new science fiction these days (although he has collaborated on some stories this century and has made guest appearances at some conferences in the last few years).

https://larryniven.net/