I was prime demographic early teen geek when TNG started but gave up on it after about the third episode. After sitting through a 45 minute majestic saucer separation and recognizing Q as the ultimate writer's device to be able to place the characters in any possible scenario (as if the future and a big section of the galaxy wasn't enough) I couldn't take it anymore. I've only seen sporadic episodes of any of the series since and haven't felt driven to watch any of the full series. I suppose in my dotage when free time may not be in such tight supply I'll sit through the lot. I haven't seen any TOS in 25 years but feel like I still have them memorized from the time before TNG.
Lacking the MST3K option, x-files got my vote although I find books are still generally the best delivery method for sci-fi.