I would personally recommend new owners start with a small selection of tubes perhaps those talked about here or maybe just buy something at random and see how it goes
Experience is important particularly if the owner is looking to tune the sound in a specific direction
Cheap tubes that turn out to sound the way you like always give the greatest satisfaction
In my own experience I really like the bass delivery of the 6680 but the detail with the Ten 12au7 is also excellent
Enter the Mullard the bass is not as good as the 6680 and the detail not a match for the Ten but across the spectrum the Mullard is superior more of a complete package
Value is hard to quantify the 6680 cost $5 each and the Ten $20 each and many great tubes including the RCA 5814 can be found for under $20
However I think for those not really interested in tube rolling who just want the WA7 at its best the Mullard is close to "end game" and worth the price
Now we just need someone to try some Telefunken ECC802S , hang on to your wallet