Just to amplify BMathew's explaination a bit. The greater the dihedral, the less yaw (rudder authority) it will take to produce a given roll response and the less "barrel" there will be to the rolls. The more dihedral, the more the plane will try to right itself from inverted and the more difficult it will be to sustain inverted flight. The trade off between the conflicting objectives of inverted flight capability and near axial roll capability will determine how much dihedral is best for you. If your reflexes are faster you can use more dihedral than if your reflexes are slower. Low dihedral aileron ships don't have to deal with that dilema.