Napoleonic, my first would be the Marins de la Garde. However, McEwan took them. My second favorite are the 3e Grenadiers-a-Pied de la Garde Imperiale "Old Guard Grenadiers"
THe guy who painted these desveres kudos. Insane detail.
Now, as for American Civil War, my favorite would have to be the 33rd New Jersey Volunteers, 2nd Zouaves "Mindl's Zouaves."
The wore exquisite Americanized Zouave uniforms.