I won't tell about repack, but more about expensions. I prefer Mop but before the Vale of Eternal blossom was devasted.
The difficult part is that each extension has a functionnality, a gameplay for one or many class, or other thing that I can love or hate. That's why it's very difficult to choose one expansion and one repack.
For example, My favourite raids for nostalgy are molten core and blackwing lair. My favourite raids for gameplay are those from Mop. My favourite BG are Alterac valley and Eye of the storm.
My favourite gameplay are Mage spe fire in wow classic, druid spe heal in Wotlk, Paladin spe heal in Cataclysm, Paladin spe tank in Mop, etc.
My favourite features are the talents tree from classic to woltk, transmo (Cataclysm and legion versions), the fly mounts, the pokemon mode and multi loot at Mop, Garrison at Wod, ...
As you can see, each expansion has one particular thing in addition to others. But, I don't like the quests at Wod, the story after Mop, the talent system since cataclysm, the instance or raid since Wod, the farming, the reputation, the extension of the world after Mop, the other races at Bfa, etc.
Sadly, it's impossible to have THE repack with everything I love in Wow and without everything I don't like.