Best 6550 regardless of price

I searched for this one and found only under $50 per tube. I was wondering what is the best 6550 not KT88. However the thread mentions KT-100s. Can any tell me about these and where you can get them. I have owned KT-90s so I am very familiar with those no need to discuss that. In addition If there is an outstanding non SS sounding 6550 where do you find that.