Hard to decide the best, there is so many classy looking uniforms back then.
I must say Swedes had damn fine uniforms back then, the main color of the uniforms for infantry was either blue or grey. Finnish regiments commonly used grey (except Österbottens and some other which had same as Swedish ones). The hats make you look like a true gentleman.
(No personal bias, I swear)I must also say that I also love what Dutch and Nassau light infantry had in 1815. I love green color in the uniforms.