A.H. Hirsch 16 Year. There is absolutely nothing else even close. (The 16 is, for some reason, even better than the 20 year, which I find overly hot even at the same proof.)

Unfortunately, there's only a limited supply of the stuff - the distillery that made it (Michters) went belly-up. All that's left is this batch distilled in 1974, bought and bottled by a Mr. Hirsch. It goes for about $100/bottle online; a few years ago you could find it for $60. I keep one bottle sealed in storage and always buy another one to replace it when my open bottle runs out.