We use tags and it works great.  It's easy to use, lives across milestones, and easily editable.  We enter "buildnnn" where nnn is the build number.

Just remember that you will want to start with 001 because build1 will also bring up build 10, 11, etc.

Because you're already in the tag field, it's easy to load it up with other valuable information like - TestReady, NeedsReview, etc.