That's completely up to you and your preferences/site.
If you're just using a forum with phpBB, you might want to use the phpbb focussed one.
However, if you also have an entire site around it, it's debatable.
Also if you've already submitted your sitemap for a while, I don't think it's smart changing it, but I am not an expert on sitemaps.
The CDB is C
ase. A database of extensions for phpBB which have been validated by their Extensions team, which means the code is solid.