It might be helpful (maybe not) to explain a little more why I'd vote for "A"

"A" is dime-a-dozen, true, but it's one thing to say it's old and familiar. It's another to say it's old and familiar done thoroughly and right. A "generic" S&S setting with fine ground-level-detail, detail along the lines of Harn or perhaps Wilderlands or Ptolus, would be something a group could either jump into or grab modules out of and just use with very little prep.

"B" is also pretty cliché, but it sounds just different enough that groups are going to have to learn them on the setting level, and possibly do a fair amount of adaptation on the module level. The motivation and drive to learn a "B" and use it for actual play is IMO in short supply, and a lot of it is already monopolized by the likes of Glorantha, Tekumel, Harn and perhaps a few other engrossing settings such as Talislanta or Jorune.

If you want to break into the "B" market, I agree with other posters, you need to really pump up the uniqueness and give people a reason to make the effort to dive into your setting.

Thanks for the feedback, I've decided to go with Setting B. It has more for me to sink my teeth in as a writer, though to be honest it may not be better for the Friday night pick-up game.

As per the suggestions to make it really unique, any uniqueness will come from being what it is as excellently as I can make it. I certainly won't try to to give it an angle that can be summed up in a sentence - like degenerate mermen fighting a robot empire, or airship-dwelling dwarves in a post-apocalyptic world. Pick-and-mix "originality" for its own sake is just not my bag.  My favourite settings - Talislanta, Atlantis the Lost World, Artesia - gain their quality from the accumulation of their parts. Sure, I could say that it is dark sword and sorcery in a doomed world - which is fairly accurate - but that tagline is pretty meaningless without the details, and it may or may not be unique enough for all you neophiles.

Look at it this way. The blurbs on the back of a Jack Vance book are generally bullshit, despite clueing the potential reader in on the general conceit of the Dying Earth. It's his brilliance as a writer of prose and the imagining of details which sets the works apart (he stole the theme of an aged and decrepit Earth from C.A. Smith after all). That's the kind of thing I aspire to, however successful it ends up being.

Guess this sounds slightly defensive, but I'm looking to put out a niche product here, practically a vanity project, not to reinvent the wheel. And one of my pet peeves is the idea that if you give your setting some unifying feature that you could create with a random generator (Romans in the jungle or Mongolian nomads with steam trains) you have suddenly made something unique and cool.

Actually I agree entirely with that last sentiment. "Clumsy mashup" is the term I use.

And really, the rest, too. The devil's in the details.

Best of luck in your project. BTW, I'd rather see BRP than MRQ.