recaptcha is the most secure captcha solution at the moment.
The "problem" is, people try to write programs to crack those captchas automatically for spamming and so forth. The project stiltwalker from the defcon 949 group ( http://www.dc949.org/projects/stiltwalker/
) cracked recaptcha some time in the past and recaptcha had to improve. Now it can be very "difficult" sometimes to get the right words. But it's no solution to move to a less sophisticated captcha solution.
recaptcha has a small little reload button, and users should just click on it a few times until they see one they can recognize.