If you are looking for simplicity (which some call "beer and pretzels" rules), the best I have ever used, and still use to this day is Rally 'Round the Flag, published in 1976.
For example:
The rules are pretty simple. Since almost everyone uses a rifled musket, the firing range is the same.
When a charge is called, the attacker and defender both take morale tests.
All the information you need, such as casualty tables (fire and melee), movement table, morale modifiers, etc. are all printed on one sheet of reinforced paper.
We used to play ACW battles on a ping pong table with 6 people (each commanding a division) and finish the battle in an afternoon.
