BDO is still incomplete, so comparing the two games seems unfair.
BnS release in multiple areas already, and with NC Soft at the helm of another release I imagine it will be a popular game, I personally don't like how they are gating the NA release similar to what Trion did with AA but here's hoping they have a better time of it.
If they come through with the PvP Tournaments and everything is in place with out any major issues before BDO release that will be a big draw for its player base. People looking for a great PvP mmo experience with possibility for a competitive scene have few options at the moment, GW2 is close with competitveness, and AA has good openworld pvp mechanics and similar style arenas 1v1 3v3 with gear standardization (in 2.5).
BDO is a bit of a different game its not focused on competitive PVP more on the game experience and open world PvP. They have some arena type pvp but its not fully fleshed out yet. The siege and Town ownership mechanics and Guild Wars system are where most of the PvP in that game stems from.
So the question I guess your asking is do you think competitive arena based combat including 1v1 and 3v3 has more lasting power then Guild Vs Guild objective based open world pvp? I guess it depends. I like largescale pvp and with the right community BDO could be amazing I really enjoy the combat system and the beauty of the game. BnS has the hype and looks to be releasing soon I think it will be an enjoyable game and hope that we can see an e-sports scene in an MMO again. If that happens BnS should have sticking power to Buy Blade And Soul Gold. Arena combat has the advantage of being on your own time and should be popular among moba players as well, which is a large playerbase.