mid 80s to now.
Cars no longer rust as bad, most have good handling, cars have decent suspension and ride quality, later on every car has very good power even basic models, every car is comfortable and easy to drive.
There is a reason why some cars early than the 80s are sometimes called "a more modern car" when discussing them, because cars from back then and earlier were almost all terrible.
If I were to pick a 10 year period it would be 1986-1996. 1996-2006 would be a close second. Why it's a second is because a bunch of good cars stopped being sold here like RX7, Supra, and Turbo Mr2 in that period. Most of the same cars are what would be considered downgrades from Asian companies but everyone else offered good cars still. Also bloat was starting to be a problem. 2006-now is third, we have a few very high power cars but everything weighs a ton and Japanese companies stopped selling decent GTs completely and every concept from them is a supercar or something lesser than what they sold in the 90s. Ie. IDX vs Silvia/180SX or FRS vs MR2, comparing to world models not what was sold int he US in the 90s.
Late 80s is HIGHLY underrated for cars. Fox Mustang, C4 Corvette, MK3 Supra Turbo, Z31 300ZX, FC RX7 Turbo, Mr2, E30, 190E, M5, Civic CRX, 944, Galant VR4, Starion, Celica Alltrac, Buick GN, etc. All of those are awesome. In the early 90s you have almost all of that but improved. Best 10 years ever.
Overseas that period is even better and now they are gradually becoming more and more legal for import. In a few years Escort Cosworths, GTRs, cheap FD Rx7s, Delta Integrale Evos, Euro M3s, a rally homologation car from every Japanese company, Stagea 260RS.....