I favour multiple stacks unless it's an early rush. If you try for more than 1 on an early rush, you eat too much time, and you lose advantage of the rush.
Minumum standard for multi stacks is dependent on diplomacy :
A - if you got your target to fight another war with an AI, then 2 stacks of city attackers/garrison. Your target should have spent its main Stack on the other AI.
B - if you cannot get them to declare, then 2 stacks; one defenders/pillagers and one city attackers/garrison.
Option A is self explanatory. The target does not have a strong counter stack because it was used against the other AI, so you can concentrate on taking citys with a combo of siege, city attackers and city garrisons.
Option B requires the target to be mislead into attacking the defensive stack while the city attackers/garrison moves to their target. Use the defenders stack on suitable defensive terrain with suitable promotions, and try to make them come from the opposite or diagonal of the city stack. You will proabably need to move the defender stack a few moves into AI territory, and you will probably need to sacrifice some individual units by moving them out of the stack as bait. I have noticed a few times a defender stack being left alone until I dangle the bait. The pillagers are best used for bait, especially a few old horse archers or chariots (low XP value if killed).
Minumum standard for multi stacks is dependent on diplomacy :
A - if you got your target to fight another war with an AI, then 2 stacks of city attackers/garrison. Your target should have spent its main Stack on the other AI.
B - if you cannot get them to declare, then 2 stacks; one defenders/pillagers and one city attackers/garrison.
Option A is self explanatory. The target does not have a strong counter stack because it was used against the other AI, so you can concentrate on taking citys with a combo of siege, city attackers and city garrisons.
Option B requires the target to be mislead into attacking the defensive stack while the city attackers/garrison moves to their target. Use the defenders stack on suitable defensive terrain with suitable promotions, and try to make them come from the opposite or diagonal of the city stack. You will proabably need to move the defender stack a few moves into AI territory, and you will probably need to sacrifice some individual units by moving them out of the stack as bait. I have noticed a few times a defender stack being left alone until I dangle the bait. The pillagers are best used for bait, especially a few old horse archers or chariots (low XP value if killed).