I really like the sound at 50/50.
For different stuff I like to use 100% on each side.
Clean, blues, dirtier blues I like the EL84's.
For more drive with a pedal playing hard rock and metal sounds the 6V6's "tighten" up the tone and response. Seems to have a quicker attack with a bit more control over the speaker in terms of damping, which is great for chunka chunka chords and riffs.
On my Rebel 30 if I turn to 100% EL84 the volume drops only slightly from middle position.
But, if I go 100% 6V6 the volume is noticeably quieter from the middle setting and from all EL84 setting.
Generally 6V6's are lower power output compared to EL84's, so that might the reason.
But, I'm hoping it's not a cold bias on the 6V6 side.
I've never done biasing so I may have to have a tech check it out.
BTW, so far everything works on my Rebel 30. I can hear the change in tone and a bit in volume when going from 1 watt to 30 watts.
Some say they hear no difference. Don't know why. I can easily hear the difference at I'm not playing anywhere near loud either.