Who will be the top girl group if or when snsd leaves?

I'm sorry if a thread has been posted like this before but I've been wondering about this for a very long time,
and I wanted to get your guys' opinions. I just can't imagine kpop without girls' generation since I've always known about them
ever since I got into kpop. Also I don't think any girl group will be able to match or beat the success of snsd either but I just
wanted to know who would be the top girl group if they ended up leaving.