What's the best forum software (free or paid) that is good in weeding out spammers? I used to manage a medium-sized forum, but I had to ditched it. The spam registrations was too much for a single person to deal with. I may do a forum again in the future if I'll find the best forum script.
We are using Invision Power Community. They have a cloud-based antispam service which works on all their network of sites. Also there is Google Recaptcha and its pretty good on fighting spam. Also you should impose some rules on when users can post links, how many links per post, banned words etc.
You can try UserPro community plugin, it allows you to see spammers by the email and it also has reCAPTCHA. You can integrate it with other plugins which are specific for fighting the spammers.
ALL forums are subject to spam registrations and each had different means of dealing with it, either in the core or as plugins/mods/add-ons. Choose your forum software based on other things you are looking for, and then investigate means of dealing with SPAM. I use SMF 2.0.15 (Simple Machines Forum) and between the registartion questions, and the anti-spam mods (you might think of these as plugins or add-ons) httpBL and StopSpammer. Some weeks I may get hundreds and hundreds automatically turfed, and as many as 25 in th e'approval queue'. These latter are ones which are probably spammers, but require manual intervention to assess. It's easy to ascertain if these are spammers and I can deal with that in a minute or so in all. Super easy. As a result I haven;t had one single successful spammer on the forum in the last 12 months.
I would suggest you XenForo with this Plugin : https://xenforo.com/community/resources/anti-spam-by-cleantalk.3975/ And This : https://xenforo.com/community/resources/block-spam-completely-with-no-addons.4065/