Sucuri requires you to change the DNS settings of your website in order to implement their WAF and DDoS protection service. WebARX runs on the application level which also means we do not provide any kind of DDoS protection.
Wordfence is mostly running on .htaccess rules. We have an actual WAF looking at all requests (POST, GET, uploads etc.).
The firewall is just one part of WebARX. We also do monitoring, scans, security alerts and the actual dashboard gives you much more value.
We believe that just a silver-bullet solution do not really keep companies secure since they will start avoiding the issues and think that something is proactively protecting from everything.
WebARX will give you the whole overview of security and improvements, the firewall is just something that buys you some more time.