Seeing as...
...Dru's post covered most of what I wanted to say, and probably in a clearer and more concise manner, I'll just add a few remarks to his list.
Re: Star Trek (OS) --It made SF on TV viable as adult programming, as opposed to a kids' only genre . It was the most well-rounded show of the list {excepting possbily Dr. Who}. While its not original, per se, it took decades worth of SF themes and addressed practically all of them in a 3 year TV run. It was at times an action show, a space opera {well, as much of one as its budget would allow}, Cold War parable, political allegory, drama, comedy, psuedo Greek tragedy, etc. It satisfied the requirements of drama: to wit, it explored the human condition; the requirements of "serious" SF: both examining/opining on the impact of technology and changing cultural mores and using SF tropes to to recast time-honored dramatic inquires into said human condition; and finally, it satisfied the requirements of "pop" SF; big spaceships, cool devices, Mongols in Space, planet-eating Doomsday Machines.
Admittedly, it did all of this with varying degrees of success, but at least it tried. Plus, it sported a cast with real chemistry, which is priceless in an ensemble show. ... And that's why its best.
Re: Dr. Who: --Drew nailed it, its fun. Even with its BBC-sized budgets it created a sense of wonder. Part of the appeal of SF has always been that wonder; that voyage into the exotic, which is couched in scientific terms, but doesn't require a whit of actual science --which Dr. Who gleefully had none of. Reverse the polarity of the neutron flow my *ss...
What it did have was wit and charm, occationally even powerful drama --I'm thinking of the shot of Adric's Mathematics Badge right now with a tear in my eye. And it evolved; from a children's show into something else entirely.
Re: Blake's Seven: --This was my first exposure to SF set outside the dominant authority system --that didn't feature an idealized, romanticed "rebellion". Its the anti-Star Trek and anti-Star Wars. Here the Federation are a bunch of bland, media-savvy fascists who employ lithe dominatrixes as Space Commanders, where the sentient computer is a annoying little box that everyone despises, where the "noble" main character disappears after season one leaving the cold-hearted, logical, all-too-nastily-human embezzler in charge. Blake's is a bit of a minor revoution in SF TV; as Dru said, meanspirited , bleak, without much nice to say about the human condition. Like Farscape after it, it traded heavily on inverting SF conventions. But its more than that; its stucture allowed for real conflict between the characters, and conflict=drama...
Re: Star Trek (THG): --Its an invaluabe step in the evolution on televised SF drama, but also something of a misstep. Often it was like an office drama set on a starship --a friend of mine called it L.A Law in space {didn't Corbin Bernson guest-star as a Q...}. It tried to be so adult, so much like any other contemporary adult drama {even during plots when the crew faced the extinction of of the human race} that they took a lot of the fun out of. Their writing staff wasn't up to the level of sophistication they were shooting for. Too often TNG was a clunky fusion of SF and conventional dramatic modes {SF drama tends toward the operatic, the "cosmic" while contemporary drama tends toward the neurotic microcosm...}. I so missed Kirk's solilliquising, his emphatic internally-rhyming ultimatums.
That said, it did have stand-out episodes, like "Darmok", "The Inner Light", and "Measure of the Man. It did what its predeccesor did, addressed SF themes, covered a lot of subgenres, even managed to innovate from time to time, such as in "Inner Light", which used a SF device to explore the soul of single character --instead of making broad comments on human nature, and "Darmok", which fused the SF classic "Arena" with a lesson on literary criticism.
I just wish the show wasn't so bloodless.
Re: B5: --I loved it from the start. Its the greatest space opera ever filmed. It embodies the SF experience for me; grand ideas, grand adventure, a fully-realized "other" world to visit, as well as the downside, frequently shoddy technical execution. JMS's speeches soar, his mundane dialogue often makes me wince. If JMS would have had some more help, like his very own D.C. Fontana or Robert Hewitt-Wofle, I'm pretty sure B5 would stand alone. As is, it was one hell of ahievement, there was and still is, nothing else like it.
Re: Farscape: --What's not to like about a well-done postmodern pulp sci-fi show that resembles nothing so much as Buck Rogers blended together with Pulp Fiction --complete with frequent untranslated swearing? A great SF show that doesn't give a damn about science at all; it merrily concerns itself with all the props and cool gadegtry; spaceships, yellow-light spitting ray-guns, currently requisite black leather fetish/flight-wear. A slam-bang adventure with a shocking respect for its characters --despite how it humiliates them-- and for psychological realism {no matter how perverse the action got, the show rarely lost its emotional moorings}. For my money, Farscape isn't just one of the greatest SF shows EVAR, its brilliant commentary on SF as a genre, an exploaration of the different appeals of SF {I could have swallowed my toungue when D'Argo admitted he "just liked blowing things up" with his spaceship}, a rare example of metafiction that also satisfies on the gut level of character and plot... blah, blah, blah. But, its unconcerned with many of the traditional functions of SF narratives, so it can't be the best.
Re: DS9: --Why isn't this on your list Dru?!
If you agree w/me that STG was an unwieldly attempt at raising the level of dramatic sophistication for SF TV, then keep agreeing that DS9 was a smashing success in doing just that. Nothing in DS9 is new; in terms of innovative SF ideas, they were fresh out. No brave new worlds to explore, so the writers focused on the characters, on ongoing conflicts ripe with dramatic payoff, on the fundemental elements of dramatic narrative. Its SF drama done right; its functions equally well as soap-opera and space opera. Plus, it had the polish, the consistently good dialogue, the more evenly-distributed acting talent that was missing from B5. DS9 became just as much an 'SF novel for television' as B5 was, and in an odd way, the strengths of DS9 had little to do with the SF bits. So it really can't be the best SF show ever, but I'd argue its pretty close to the best TV drama EVAR...
I'll stop now. "A few remarks"... I make myself laugh sometimes.
