If I had to compare combat? Black Desert is like Vindictus while BnS is like TERA. I haven't played BDO, but I know BnS doesn't have a dedicated healer/tank class; everyone is dps. Classes can slot in aggro generation in their skilltrees at least though and KFM (Kung-Fu Master) and BM (Blade Master) are the "tanks" in the current meta. Each class has some level of support, but some are better support roles than others.
BnS also has ranked arenas, 1v1 and 3v3, and is even part of the eSports scene in Korea. Right now, I can name you the Imperial Network as a PvP community tournament--one I'm personally looking into from an event organizer standpoint--for the NA/EU audience.
I'd say go to BnS if you don't mind some linear leveling and want to PvP. If you'd rather have a sandbox and visually pleasant experience, then take a look at BDO. You're looking at a theme park (BnS) and a sandbox (BDO).
No idea, but I think BnS even has an RP community in the works? Seems all over the place imo.
