Great ideas in this thread for sure!
Are you guys picking units from different lists or just using a standard list, but being very deliberate in what gets upgraded/downgraded into Raw/Veteran (if list permits)?
We've just been picking and choosing. I use 'warriors' (deep units with heroes) for large orcs and lizardmen; 'mobs' for smaller orcs; veteran billmen for ogres and trolls (with trolls as fanatics to represent regeneration or stony hides); and then any historical units just plucked from the relevant list. So we just dump in Assyrian cavalry ('evil men') from the Assyrian list to match the miniatures alongside 'knights' and 'later knights' from the Crusades and WotR lists.
I also used 'cataphracts' for orcish boar riders; the higher of disordering while on manoeuvre represents the obstinate mounts!
Do you know if the List's point values are universal, so you can pluck statlines from anywhere? or are they costed mostly for the army in question?
I think they're universal; certainly, we've had nicely balanced and exciting games from the pick'n'mix approach.
All of Elbow's points above are great; I'd add that TTS feels like quite a 'zoomed out'/abstracted game (and is all the better for it), so worrying about whether (e.g.) dwarves are tougher than men and slightly slower doesn't really apply. When we use 'veteran billmen' for ogres, the obvious thing is that the ogres are much bigger and far fewer than actual billmen, so everything feels about right.