OK,
first, define 'classic'.
Since you did request best performance then aesthetic appeal should be secondary .
From the '60' I'll go with the Taurus and the Kwik-Fli, based mostly on their popularity as I never flew either design.
Joe Bridi's Kaos was sort of a landmark design and resulted in several more excellent Bridi designs (I think the Kaos appeared around 1971??).
Jim Kirkland's Intruder design flew well, but it was his 2-part article in MAN which included detailed information about flight trimming that really makes it notable.
The legendary 'Tipo' may have been the most popular design ever (at least here in the USA).
The EU-1A had a substantial following, especially in the Northeast where I can remember seeing 10 or more show up at local contests (I think it was Jeff Urcan, Lance Murphy and Art Fressola who got the 'movement' started, the the RI contingent had some <Dick Dupres, maybe others>; Don Krafft had one, the Canadians who came down from Nova Scotia <Dave Smith for sure> and some I can't remember). The EU-1A presented really well (geez, it was huge at the time), but hot and/or windy weather was the major achilles heel as they tended to be heavy (10+ lbs) and as a result suffered a bit in the power department (but, those Rossis really worked hard). Hence the nickname EU-ton.

I'm going to define 'best performance' as longevity with the original designer and a high level of success, for the sake of arguement and so I can justify my list
Arrow - Matt liked it enough to fly the prototype in 2 World Championships and whatever competitions in between (more than 2,000 flights on it at the '83 WC)
Silent ST - Naruke flew the same design (I don't think it was the same airplane) from '87 to '89 or '90 (again, in 2 WC)
Mistress - Dave von Linsowe flew his .60 powered design for 3-4 years in the mid '80s with consistent success (top 10 finishes at the Nats)
Malibu - Bill Cunningham campaigned his design for several years as well

This is not necessarily my list of personal favorites, either!

-Will Bartlett