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The question is what type of sonics are you looking for from your amp?

I was very pleased with the Brimar CV4003/12AU7 from Upscale... provided warmth with extension. When I changed my power tubes, I went with NOS Tung Sol 12AU7’s which provided transparency and realism. Fantastic tubes and affordable.
Have also tried RCA 5814, but they were better suited for an input gain stage due to their wonderful timbre.

In a power amp the tube or tubes in the gain stage have the most influence on sonic signature. I've been told that the driver/phase inverters have little effect on sonics; eg, timbre, dynamics.
Not so, IME. The tubes in the driver stage have an audible influence on the sound (depending on the design of the amp). 

I'm in agreement with all the comments thus far to choose a good NOS tube for this stage even if it's purpose is simply to drive the power tubes.

What is the make and model of your amp so we can Google it.

The M125 monoblocks...
http://www.tubes4hifi.com/bob.htm

There are indeed only 2 driver tubes on each monoblock. If I’ve read this correctly, the driver stage generates higher than typical voltage, so there isn’t a separate gain stage.
The sonic effect of the driver tubes will be significant.