@yogiboy On my Quicksilver amps I can use both types. I prefer the sound of the KT88 compared to the EL34. It all depends on the speaker that you are using. I find that the KT88 sounds bigger and brighter than the EL34!
+1 yogiboy. 100%, so true. Was just sharing this on another thread about this, its a fact. Matching to your preferred sound is key, all speaker dependent for sure.