Great question... Got myself a Klein Pinnacle frame with my Saturday job money when I was 18. The step up in class from the Reynolds 501 Peugeot I was riding at the time was ridiculous and I am still riding it, issue free, 25 years later - big thumbs up!
Also, recently aquired an NOS '99 Yeti ARC and it instantly made me think (rightly or wrongly - I'm sure there are many candidates for this accolade) that I'd got my hands on the what must be the best alu hardtail ever made. Amazed at the difference in rear end compliance compared with the Klein and it basically feels like perfection on wheels - I think it helps alot that it's a perfect fit too.
Briefly owned an Ibis Silk Ti too. It's undeniably awesome but the fact it was a bit too big for me and four times the price of the Yeti made me sell it on during a skint period. Breathtakingly amazing, yes, but I was able to part with it without shedding a tear.
The one I'd love to try but never have is a small Yo Eddy. Maybe one day...