I might consider that once I can design my blog site and MyBB forum to have matching headers to change to /community. You have really great considerations. What is your personal user preference of owners having a forum as a subdomain?It depends on if you want to work on making the two look and feel part of each other, or if you just want the community separate from the blog.
If the goal is to make the two look and feel a part of each other, then I would recommend it on the /community/ slug, with the designs similar enough to be able to feel like you aren't on a completely different site. Of course this way, you would need to have designs pretty close to each other (colors and headers being the same), with the navigation allowing access to both the blog and forum from the same area.
I know both work, but I am seeking user preferences and suggestion for either option of a subdomain.Any subdomain provided above would work.
community.domain.com or domain.com/community