Here's the question; given 1000 points, and the models of your choosing, what would be your go to for the two armies listed (I'm thinking Minas Tirith and Fiefdoms vs Mordor without allies).

What would be your lists!?

Depending on the scenario but I'm leaning Mordor purely for hoard reasons. A will point heavy ringwraith can deal with boromir, though Gandalf the white might prove tricky at that points if he's on the board.

I can speak with more authority for Mordor because I've been reading tons of articles and have played them quite a bit.

There seems to be a few playstyles:

The beginner-Med player

I'd definitely start with Shagrat, the more expensive version with a shield.
For forces, I'd go with Morrannon orcs with shields (D6) and back them up with regular orcs with spears to support them.
Blackguard are overcosted unless you are facing high D models.
Trackers are a cheap archery unit for orcs and can be used instead of regular orcs with bows.
Shamans are essential for Fury. Drummers can be great for movement (so you are not picked off by archers, every turn)

The Med-Pro player

The 'Ed': Fellbeast army with Darkmarshall, Betrayer, and another ring wraith. These two named wraiths seem to punch quite a bit and the fellbeast is currently undercosted (in the opinion of GBHL writers)

Tight Formation: Using strategic ringwraiths like the Shadowlord to provide cover or the Darkmarshall for banners to slowly move up the field and play around objectives.

The Swarm: Employing tons of orc contingents with cheap heroes and shamans. Again, positioning is important so you're not picked off. Professional positioning of Gothmog can counter many heroes that rely upon heroic calls.

I can't give you any specific lists for Gondor, Boromir is a fantastic hero with 6 might. Alternatively, the fountain guard boast great defenses.