Allow me to give a different perspective.
I was a big fan of X-Files when it debuted. Sunday nights were blocked off to watch. The first two or three seasons it was the can’t-miss show of the week.
By contrast, I openly ridiculed Buffy the Vampire Slayer when it was on. I never watched the show during its run. My wife was an avid fan, and she occasionally would try to get me to watch. I would mock her incessantly.
But something interesting happened. It became fairly obvious to me (as it did to most everyone else) that XF not only couldn’t deliver on its buildups, it adamantly refused to do so. Cliffhangers were introduced and then ignored. I became disgusted with the show, and bailed early (even before Duchovny left).
Even die-hard XF fans acknowledge the mess the show became. Sure, its stand-alone episodes were good. The problem was, the show was based on a single arc, and it never resolved that arc; in fact, it had no plans to do so.
And for Christmas one year, I got my wife the first three seasons of BtVS on DVD. She convinced me to watch the first four or five episodes of Season 1; after that, she said, she’d quit asking me. So I did. And I got hooked – the year after the show went off the air.
Yes, BtVS was chock-full of teenage angst. But the characters hooked me, and the writing was superb. What’s more, the show’s creators didn’t treat the fans like crap and insult their intelligence, as I feel XF’s did. So, to me, BtVS is by far the superior show.
Now, in my estimation, Angel far surpasses BtVS, but that’s another discussion.