My opinion is that the Funcaptcha is the best.

But you should combine the captcha with other solutions to get a effective security system. Bots use Decaptcher services to solve any captcha.

You should study techniques as:

- Real antibot links.
- Use services to avoid proxies and malicious IPs as NastyHosts and GetIpIntel.
- Use .htaccess to block proxy servers, countries and to blacklist malicious IPs.
- Use a slice/slide button in the place of a simple click claim button.
- Use some timer before enable the claim function.
- Using a second captcha or puzzle to enable the claim function.
- If you are using Funcaptcha, enable the Enhanced protection mode.