The best solution is something that's unique to your service, and doesn't exist on any of your competitors. Remember that automation is only cost effective at s

The best solution is something that's unique to your service, and doesn't exist on any of your competitors. Remember that automation is only cost effective at scale, hence bots are written to target commonly used systems rather than those bespoke to any one particular site or service (unless said service is FAANG level popular). So a captcha like setup that's specific to your site, various timing based detection systems and some hidden fields would probably work better than something like Recaptcha here, assuming you never become as popular as Google or Facebook.