I'd have to say the 1970's, not so much because of whiskeys I've tasted in recent years made then, but because of what I remember from drinking whiskey at the time.
I remember that Maker's Mark was superlative. I remember Old Yellowstone with its rich fruity taste. I remember the rich, dark rum-like Benchmark. And Old Fitzgerald 80 and 86 proof (the regular age) with a fine medium caramel-like taste, and Kentucky Tavern when a rich whiskey made by Medley - and ditto Ezra Brooks.
There are many fine bourbons today but those particular taste profiles seem hard to recapture. A noted exception is the current JD I've been discussing, it has 1970's quality, IMO. But I like many bourbons of today too (many from Four Roses, Rare Breed, Evan Williams Single Barrel, EC 12, Weller 107, BMH 18 rye, the A.H. Hirsch bourbon bottlings when available and numerous others).
It is not so much that the 1970's were great as such, but that particular choices were available then that seem largely absent from the market today, particular taste profiles I liked. Whereas the taste profiles that are available today must, I assume, also have been available in the 1970's (or mostly so, setting aside perhaps super-aged bourbons, but they are not my first choice). This would be I think because there were more producing companies then so there was more choice overall.