All of the "multiple choice" versions are prey to the spammers simply trying a random one. At the moment they don't because it's not worth their effort, but as more an more sites use the "Odd one out" or "What is ... :A, B, C" type CAPTCHA the spammer will simply scrape the questions and put a random answer. The odds are good enough that it will be worthwhile.
However, for now that method does work. If you use it, though, modularize and be prepared to change it later.
And for what it's worth, I find the existing CAPTCHAs infuriating, and I only tolerate them if I really want the service they're protecting.
