[forgotmypw17]

I think it depends on who your audience is.

For "general" audience, I would use a proof-of-work puzzle 10 seconds long and a basic question captcha with human review.

But for a site which is primarily for tech-savvy people, with an accent on retro-compatibility (HTTP auth is supported almost universally, even by Mosaic), I can't think of a better option. Not that interested in SEO, since the software is my main target.