I suspect the answer depends partly what you want from TV and partly when you grew up.
Personally, I don't like "investing" in TV (I don't generally like having to watch a show regularly to follow a storyline, esp. if the storyline extends beyond a a handful of episodes) so I naturally gravitate to more episodic, and light-hearted, television. Sitcoms, action-adventure shows, the occasional soap (soaps are paradoxically very easy to drop in and out of), what are now called "procedurals", that sort of thing. So obviously, the late 70s through to the late 90s are always going to appeal strongly to me.
It's an open question whether my preference for that sort of TV is cause or effect, given those were years I grew up in and developed my preferences. There are some modern series I quite like, but they fall in the same camp of being ones you can idly dip in and out of and it doesn't really matter if you've seen any other episode (the CSI, NCIS type of show) though I'm sure they also drop enough light continuity to appeal to that type of viewer . But plenty of people my age prefer the more serialised types of show, so I think it boils down more to how you actually watch TV.
If you're a channel-hopping grazer (like me), the odds of watching the same show every week are pretty low and even if you do, you'll be multitasking with something else so are unlikely to give it enough attention to follow a complicated plot. If you actually watch TV (as in tuning in to certain programmes at certain times, or DVRing them, or buying/renting the DVDs), then I think you'll probably tend to prefer series that try to tell a longer story. Since there seem more of those these days, they'd probably prefer late 90s to current TV, I'd guess.
