A similar topic was discussed years ago:
http://www.rc10talk.com/viewtopic.php?f=39&t=32910
The Yokomo Dogfighter was the first 4WD car designed for racing, but the Optima was a game-changer and was arguably responsible for causing 2WD and 4WD racing to be segregated into separate classes. Up to that time, 4WD cars were relatively heavy, slow & clunky and couldn't compete against RC10's and other 2WD cars, so they were allowed to race together in mod class. Then the lightweight Optima came along with a fantastic suspension--especially with Kyosho Gold shocks--and the 2WD cars could no longer keep up, unless on high-bite tracks, perhaps. In the Tower Hobbies catalog from 1985 or 1986, it was stated that Optimas won 1, 2, 3, 4, 7, 8, 9, and 10th place in the ROAR Nats.
But for an "eternal winning design", I'd concur with the Optima Mid (for 4WD), as the original Optima had many rather serious design flaws; prone to understeer, chain stretching and always needing maintenance, weak final pinion that was a major pain to replace, weak front end that acted more like a crash zone than as protection...but you add the Kyosho Gold shocks and the improvements in the Mid belt drivetrain and tweaks in design and you had a 4WD car that performed as good as any. Looking at the engineering of those late 80's cars, not much has happened since to truly revolutionize performance, if you look past electronics. The late 80's/early 90's were the apex of RC car performance and IMHO, not much has been ground-breaking in the decades since, other than changing materials (plastic/aluminum/nylon replaced by carbon fiber, which is nice but not revolutionary).
I of course agree with the RC10 and the many variants as being an eternal winning design. From RC10, 10T to DS, I don't think any other 2WD chassis could so easily transform from one racing design to others and still perform excellently. (The exception being the attempts to transform the RC10 into 4WD, which was a mal-performing kludge at best...but perhaps best illustrated AE's desire to compete with the "new lightweight 4WD cars" like the Optima.) They had to scrap the kludge idea and start with a clean slate and design a totally separate 4WD chassis because trying to turn an RC10 into 4WD just didn't work. That's probably the only thing the RC10 failed at.