I prefer the Remington NMA 1858. While I handled Colts before and they do handle extremely well, the Pietta Remington's wider grip and wider frame is a great improvement in the Remington reproduction class. Actually, the Pietta model is more accurate to the original Remington than the versions by Uberti or Euroarms.
However, I choose the Remington for it's even simpler construction, and the ease of swapping cylinders on the firing line without having to use special tools for breakdown. If you are a serious competitor, the Remington will be your top choice. That or another closed frame revolver such as the Rogers and Spencer or the Whitney.
Regarding the fouling problem, that could easily be solved, using different powders, such as H777, or a homemade version without the sulfur.
I took sulfur out of my homemade BP to clear up the smoke and fouling, and have discovered, that I am getting more accuracy from my follow-up shots, since less fouling accumulation in the bore with each shot means more accuracy in the follow up shots. Very important thing to have if you are in a CAS or NSSA shoot, where timing and accuracy rules the day, and every second spent at the pitstop will mean less points for your team.