I actually found I got the furthest when, I had 4 Captain of Gondors and two Rangers.
I think the trick is to clear a room, then wait for the group to reheal.
I haven't had any issues with AI just running around, although sometimes they do attack the enemies from the back instead of those in front.
It says that some classes get bonuses, and I noticed the Uruk didn't get anything, Maybe he should get a damage boost or something.
Using the power section, which do you find most useful?
I picked the veteran for extra health and it gave me 665, I then tried the extra health for each enemy defeated and had no idea which was better.
I picked the Men of the south/West and the switch weapon doesn't work, they switch to their Bow but then run up to the enemy to attack, its like they have no range.
Apart from that I think you have done a fantastic job, its fun and the AI tend to works pretty well, I cant say I've got that far into it. The 3 trolls on the second floor is tough though.