I think these are the best characters to choose for every mission:

Gates of moria: Gimli
Balin's tomb: Aragorn
Amon Hen: Legolas
Fagorn forest: Gimli
Plains of Rohan: Aragorn
Westfold: Legolas
The deeping wall: Aragorn
Breched wall: Aragorn
Honburg Courtyard: Gimli