which bind is the latest stable release?

I did a Google search and found this: Stable release 9.11.0 / October 5, 2016
Generally speaking you can expect the Ports collection to be up to date (not always!). When looking at the Ports collection (time of writing) you'll notice 3 versions: dns/bind99, dns/bind910 and dns/bind911. What I usually do when I get started with something is to pick a version "in between". Not too old, but also not too "bleeding edge" either.

Just my 2 cents of course.
If you want something long-term I can suggest using the ESV versions. These usually are supported for several years and are stable (no new features or changes in operation). So I typically run ESV on production and the latest stable version in development/test environments.