WP Security Scan is more of a website security scanner like the name suggests and does have website security features that protect your website, which BPS also has. The most important security feature that WPSS has that BPS does not have is the WP SQL DB table prefix renaming feature to rename your DB table prefixes. This may be added to BPS versions in the future, but since BPS already completely blocks all hacking attempts to your WP DB then it is not really all that important to change the DB table prefixes. It would be more of a bonus security feature as opposed to an essential security feature. These plugins have been tested together and they do work together so you could install both of them if you wanted to.
If you ask me which plugin is the better plugin then you know what my answer will be. LOL To help make your website security plugin decision easier you should be looking at WordPress plugins that offer .htaccess website security protection. Coding function level (website security functions within the PHP coding itself) website security protection is effective and very important, but .htaccess website protection is a front line defense against hackers. .htaccess files are basically a website Firewall with the right .htaccess security coding added to them.
So I recommend that you do some general research on what .htaccess website security is all about first so that you can make a more informed choice on deciding on which WordPress website security plugin or plugins to use for your websites.
There are a lot of great reasons to choose the current version of BPS and I am regularly upgrading and improving BPS. So the future versions of BPS will continue to offer additional website security features, improvements and other features. Thanks.