I have used Siemens EL34 and SED EL34. They are sharp and have a good cutting top end.
I usually bias the EL34 in the VH4 to 30ma or 60ma a pair. It gives them a bit more room to rise and does not compress as quickly when pushing the power amp. If you have the money and want the best of both worlds, a NOS quad of Sylvania 6CA7's sound ungodly in the VH4. Big balls and a little compression when pushed. Try to run the bias a little cooler than 35mA and the amp will run a bit cooler. To my ears it sounds good especially when the amp warms up. A Diezel is at it's best after about 30 minutes of warm up or playing.