Most effective form of CAPTCHA?

Question

Of all the forms of CAPTCHA available, which one is the \"least crackable\" while remaining fairly human readable?

Answer 1

If you're a small enough site, no one would bother.

If you're still looking for a CAPTCHA, I like tEABAG_3D by the OCR Research Team. It's complicated to break and uses your 3D vision. Plus, it being developed by people who break CAPTCHAs for fun.