I don't know if it's the best, but the sexiest, and coincidentally most expensive 9 speed group I've ever seen is the Shimano 25th Anniversary Dura Ace 7700 group.
It comes in a nuclear-football-style briefcase and with a watch. I nearly bought one about a decade ago when I was making too much money, but realized I'd never be able to install it on a bike and actually ride it. It's just too pretty.
You can still find them on Ebay for just under $5000. Ridiculous, but you did ask which is the best 9 speed of all time, and I figured this deserved a shout-out.