There are a great many extremely well built saws out there and some of the saws being built today will be joining the list before long.
That being said, for me the best DESIGNED saw ever by a large margin was the Poulan 3400-3700-4000 series.
Great controls placed where they should be.
Simple to use, maintain and rebuild.
Outstanding Anti-vibe for the time and still not bad even today.
Reliable as the sunrise, given any care at all.
Still able to run with most of the saws built today given a decent operator.
They "feel" like a chainsaw should feel in the hands. (Admittedly a bit heavy by today's standards but hey, it was 1979)
Not "fuel fussy" at ALL!!!
Darn near indestructible, and last but CERTAINLY not least,
Generous automatic oiling with MANUAL OVER-RIDE!!!
Several saws had the auto/manual oiling and they ALL should still have it, but the one on that series was the best I've seen.
They were (and still are) just an outstanding design. If you have never had the pleasure of running one, get to a few GTGs and try one........just don't blame me if you find yourself perusing the "Bay" looking for one of your own!
Mike