I will say this: In late 1989 at a local track( about 5mi from where I live now) there was a local racer who did suspension work Still winning open expert on his 81 490 Maico. Kevin Stillwell I think he was. Anyway, bike was stock except for suspension-even the stock Bing carby, in fact it was ratty.
Still, he not only won, but holeshot against the local young hotshoe on his 89 KX500( which I know for sure is Waaayy faster than the 490). It was obvious that Kevin was hooking up all of the power-all around the track. To be fair, he had raced that bike almost nonstop since 81-so he was familiar with it. Months later, Kevin was racing a 90KX500( must have waited for the 90 model with USD forks)-and was not able to duplicate his sucess as on the Maico.
Now, do I think an 81 490 is better than a 90 KX500? No way, even though Kevin was clearly about 40 at the time it was abvious that the 490 just really "fit" him-and he was very comfortable on it. So, is the 81 490 Maico the best bike of all time?
I think not, the best bike of all time may not yet be built-or even designed. Further, if one had to be chosen from say 68 to present-the 74 CR125 Elsie would be the more obvious candidate-literally dominating the 125 classes( and even 100 classes when sleeved down) overnight..and it was cheap and easily available.
Perhaps it is reasonable to say that the 81 490 was one of the best open class(500 cc class) bikes ever-or even arguably the best.
Compare with the YZ465? The YZ is much cheaper, reed valve-easier to start, easier power for the novice-and at the time much more available. Yes, of course Maico did not win these championships. One wonders if Maico had such a great bike ten years earlier, perhaps they could have...but history is history..coulda should woulda. I think the Maicos are popular now since they seem more exotic than a YZ or RM. Many want a bike now that they couldn't have then-as a result it is my experience that currently, Maico parts are much more expensive, but also much more available. Personally, I would take the RV 83 490 Maico and race in the later class. Seems like everybody has an 81 490 now. But for the AHRMA GP 500 class ( pre-linkage etc) the YZ465 is a great bike, though I would go with the RM400, Hunkavarnish CR 430, KTM 420, or Monty 414 myself.
Now my fingers are as tired as my meager mind