Okay, I listen to a few bands from Switzerland, but most of them are basically the same band. Celtic Frost, Hellhammer, and Triptykon are essentially all one band. So, because Celtic Frost was around significantly longer than the other two versions of the band, they get the honors. Plus, it's damn hard to beat To Mega Therion. Celtic Frost of course was hugely influential on several styles of extreme metal. So they get the win here.