Cayin A-50T - Tube Upgrades??

I recently acquired a Cayin A-50T with all stock tubes, and very low hours of use. I do want to try some different tubes at some point in time, but only after I feel that it is broken in. Since I have quite a few 12AX7's and 12AU7's, I am reluctant to purchase any others unless there is something that would be far superior to what I have. Also, I do not have any extra EL34 quads, only some different type pairs, so I will look to purchase some new production EL34's, as I just don't care to spend what it will take for a NOS quad.

This will be my first experience with a tube amp, as I have always used SS integrated amps. Here's what I have for 12AX7's and 12AU7's,

GE, long ribbed plate
RCA, grey plates and black plates
Raytheon, black plates
Sylvania, long plates and short plates
Mullard, short plates and box plates
Telefunken, smooth and ribbed plates

Any suggestions for EL34's and which tubes should I try first?

Comments will be greatly appreciated.