Latest version of Directadmin has CSF installed by default.
Both: If you decide to use CSF, there are a set of scripts which can be used to link the BFM to CSF, so you get the best of both. It will use the iptables configuration, and all features of CSF, plus the added benefit of the BFM to find some extra cases which triggers the blocks using CSF.
https://help.poralix.com/articles/how-to-block-ips-with-csf-directadmin-bfm