I have to go with h.o.t. They had the largest fandom in Korea.
Feb 14th 2021 #3 EXOOne of the biggest KPOP groups ever.A true JUGGERNAUT. There will be no one like them. Not in this millennium.
Feb 14th 2021 Official Post #4 BIGBANGEXOBTSBLACKPINK2NE1SNSDWonder GirlsTWICESHINeeSuper JuniorRed Velvet
Feb 14th 2021 #8 Domestically? Majority are from the 1st and 2nd gens. HOT, G.O.D., scheck kies, Big Bang, TVXQ, and SNSDInternationally, BP, EXO, and BTS