Tube rolling newbie- how to choose NOS tubes

I’ve purchased a xDuoo TA-30 dac/amp for my first tube rolling experience. From online reviews, I plan to tube roll in a Matched Pair of Mullard 12AU7.

Looking online, there are new reissued Mullard 12AU7, matching NOS tubes at various price points, years, features (like long plates?), and used tubes like on eBay.. This is confusing, how do I choose? Should the tubes be tested? Who should I purchase from?