My grandfathers both died before I was born, so I would probably pick them. If it has to be someone famous, Manfred von Richthofen, and Eddie Rickenbacker at the same time, think of those stories.
I did get to share a beer with Chuck Yeager and Bob Hoover once at a Oshkosh WI Bar.
To many people that I would like to drink with in the forum for me to choose and if I had to pick one famous person then I would feel robbed by not getting another that I might enjoy.
So I guess I will be content with the group of guys I drink with every Friday night at beer and cigar night. Besides when you have been getting in trouble and drinking with the same guys for 40 years it just seems kind of like cheating on your wife spending time with a famous person
Famous people, well, many of ones that immediately came to mind have been listed (Twain, Hunter S Thompson, Neil Armstrong, but I'd also agree with Hendrix or Lemmy).
But at the end of the day, I'd have to go with George Carlin.