I have a well known hatred for CAPTCHA and on my latest EE Spotlight article, titled Avoiding CAPTCHA with ExpressionEngine, I go into the whys and hows of making CAPTCHA a thing of the past with your ExpressionEngine sites. The tldr version is to use a combination of Snaptcha, Low NoSpam, and VZ Bad Behavior to block 99.999% (totally made up percentage) of your site spam. 

Read it over at EE Spotlight.