I would suggest first spending a few hundred hours listening to your incoming Vali 2, with it’s stock tube, before you start looking at other tubes.
If it is your first amp with tubes, then you’ll want that time to get accustomed to how break-in with tubes works. And with tubes this is as much, perhaps more, about mechanical settling with the tube, as parts expand and contract through normal thermal cycling and the noises they make that are environmentally audible (i.e. not through the headphones, but just in your ambient environment).
There will be “tings” and “pings” and other mechanical noises that lessen over time. And there may be whistles and burps and noise, here and there, as the tube settles which can take as much as a couple of hundred hours to fully go away (and with tubes that are marginal, may never go away).
Beyond this …
Tube-hybrid amplifiers are generally much less affected by the tube in use than pure-tube amplifiers. So, the possible benefits (or differences, as most of the time “better” is going to be purely the product of personal preference) are a lot smaller than they are with pure-tube designs.
Don’t spend a lot on tubes for inexpensive amplifiers (you’re typically much better off investing that money in a better amplifier, especially at the budget end of the hobby). I’ve never personally heard a situation where doing so has taken an amplifier to “the next level”. Changes and improvements are generally small and often subtle.
Which isn’t to say “don’t tube roll”, just don’t go buying $100 rare tubes expecting them to turn a Vali 2 or an MCTH or a Sunrise into something like a Decware, EC or DNA amplifier.