As far as tone goes...that's entirely subjective. What sounds great to one person will sound like garbage to another (funny story about that in a minute).
Since you're dealing with a tube head, you need to make sure that the impedance on the cabinet can be matched to one of the outputs on the amp.
The Valve King can output 4, 8, or 16 ohms. From what I can see, the AVT cabinet can either be set up for 4 or 16 ohms in mono.
I'd recommend a 16 ohm setup for a tube amp. It works the power stage a little more efficiently, and you have a little less loss in the speaker wire between the amp and the head.
And now...a funny story about tone. Many years ago, a buddy of mine was an amp tech at Ray Hennig's Heart of Texas Music here in Austin (the place where Stevie Ray bought his #1 Strat). Anyway, one day the bass player for the Butt Hole Surfers brings in this combo amp he used at the clubs. The amp needed a new pot installed or something similar. The last thing he told my friend...."Hey man, the speaker is blown, but DON'T FIX IT. I like the way it sounds".
Greetings from Austin,
Ken