This is another question that comes up quite a bit so let’s take a look at it now. I like the 6V6s a lot because of their tone which tends to be on the warm side with what I consider to be “smokey” overtones, plus they also have the early break-up which I prefer as well. There seems to still be a lot of NOS 6V6GT tubes available which are my favorite as they have a smoother tone to them, and while the current production tubes being offered seem to have a bit more gain & edginess to them they also come in as a very solid tube as well.
As a rhythm player sometimes I need to have a bit more of clean headroom so that’s where the 6L6 comes in at. The 6L6 does have a later break-up as well as a bright & “chimey” top end to it’s tone. The 6L6 I prefer is the 6L6WGB which is also known as the 5881. It has about 20% less output than the 6L6GC, but it does offer the warmer tone that I like for my personal use.
Another thing to consider when deciding on which power tube you’d want to use is to how much output you’re going to need from the amp. In my opinion a pair of 6V6GT’s work very well in amps up to 25 watts, but anything above that and the tone does suffer. A pair of 6L6GC’s on the other hand can be used from 10 to 60 watts and they’ll sound just fine.