I don't know why this thread even exists but ok. I mean, I'm not a fan of either but surely it's obvious that BTS is more famous.
But then talent? Well that's kind of subjective, and people don't tend to compare boy groups with girl groups in this regard anyways. If you want my honest opinion, BTS is an older group and so they have more experience and would presumably be more talented, for example their main vocal is probably a bit better. And this isn't meant to be sexist but boy groups usually have more complex choreographies than girl groups. On the other hand, and this may just be because they're a smaller group, but each member has a specific role that they carry out - there's no one who's "just a sub-vocal". Blackpink feels more like a well rounded team than a group that gets dominated by a few members (not naming anyone).
It's honestly sort of an awkward question. Personally, I almost only exclusively listen to girl groups (so if you asked me I could actually list some Blackpink songs, but I couldn't for BTS as I hardly listen to them), but I don't get why these two groups would be pitted against each other like this by fans, they're so different.