Seeking tube 12AX7 recommendation for a Conrad-Johnson Premier 3

I recently had my Conrad-Johnson Premier 3 pre-amp restored. It sounds great running with JJ tubes, but I am interested in upgrading the two 12AX7s. Looking for recommendations for upgrade tubes. I know CJ recommends Mullards.

I appreciate any tube advice specific to this amp, but any general 12AX7 recommendations are appreciated.

The other Premier 3 tubes are 5751 (5) and 5965 (2). My tech recommended upgrading the 12AX7s first though.

The CJ is being used as a preamp (phono and CD) connected to a line-level input on a Rogue Audio Cronus Magnum II. Speakers are Vandersteen 2CE Signature IIs.
Thanks