Objectively, there's value in most eras, I'd say. Personally, I value the drivers and the personalities and overall vibe surrounding the sport more than the cars themselves, as I'm the kind of person who doesn't care much about how the engine sounds (so long as it doesn't hurt my ears - GP2 in 2014 was unwatchable in person after sitting through an F1 practice session) or the ways in which cars or individual components work, so long as they provide a reasonable, realistic, and to a good enough extent, "pure" challenge for the drivers and teams. I have no love for gimmicks like the awful philosophy behind the Pirelli tyres or this year's excessive dirty air and obscenely high corner exit traction.
The sport has to be challenging, but in my eyes, it has to have both a strong strategic element (something we're seeing more of a resurgence of in 2017, especially with Mercedes' excellent strategy in Spain) and something that can make you go "I could never ever physically do this no matter how many years of (sim)racing I did". The more balanced they are, the better.
Handling-wise, I'm okay with pretty much anything if most simracing titles are anything to go by, including the old cigars which I find to be a lot of fun. And while I don't like outright assists such as TC or ABS, I think there's significant value in the added complexity of the current cars, with AC's SF15-T also being a ton of fun. Hell, even those are completely fine in other competitions - AC's GT3s and GT2s are much more enjoyable than I expected them to be.
For individual years, I quite liked 1981, 1983-1987, 1990, 1995, 1997-2000, 2003, 2007, 2008, 2010 and 2012, though they are hardly the only ones and they, too, had their occasional shortcomings. As a viewer, generally anything from 1985 to 2008 is especially good for me, even the Schumacher years as I was the kind of kid who never minded his dominance at all given his supreme skill. In particular though, the main thing I want is for the winning driver to be a standout driver even among his peers, with either extreme consistency, a number of extreme standout performances, or both. After 3 years of seeing a slowly decaying Hamilton win (or in last year's case, lose) in an overly dominant car against a mediocre teammate in the form of Rosberg while other drivers were stuck in worse cars or out of form (Vettel), it's good to see a proper top notch driver like a resurging Vettel finally have a good enough car to make up the pace difference and provide a real threat to the championship.
It also helps if the drivers are likable and stand out enough outside of rehashed PR-centric interviews. The likes of Massa, Emmo and Patrese are good examples of that for me (Alonso, Webber, Senna and Hunt being counterexamples), with recent years having fewer and fewer interesting people as a whole due to the increased focus on PR.
Over the years, I've also found that a lot of fans, especially ones that started watching "too" long ago, tend to have a misguided idea of what the sport should be like. Old seasons were good, but one has to be careful not to see them through rose-tinted glasses and to try and appreciate what the sport has to offer in its modern years as well. More casual fans can sometimes be guilty of this as well, but mostly in the sense that they want to mold F1 into something that would only eventually serve to kill it.
