In my opinion
Groove Tubes are the best for a tube amp because of there "Reliability and the outstanding warranty". They offer a large variety of power tubes that come in grades of 1 to 10. 1 to 4 are rated low. 5 to 7 are med. 8 to 10 are high. This means 1 to 4 will distort sooner. 5 to 7 are average where 8 to 10 will stay clean almost to peak wattage.