What tubes fro my el84 amp?

I recieved my first tube amp today and would like to know what others are using. It has a pair of 6cg7 drivers (rca) and the pwr tubes are russian (quad). The amp is actually a intergrated with only one input so I'm using my tube ASL pre for my other sources. My other question is what would make the greatest difference in sound the drivers or pwr tubes. At the moment I like what I hear but--- Stay thirsty my friends.