Wow, there's so many variables that you are sure to get a lot of opinions. What it really comes down to is what you wish to do in western shooting. Do you want quick draw? Target? Cowboy action games? Do you want the gun to be built to period specs, or not?
My preference are the period correct versions of the Pietta 1858 New Model Army (.44cal) or the New Model Navy (.36cal) in either the 5.5" or 8" barrels. 8" barrels aren't so good for quick draw though. Others may prefer the Colt varieties, but it's the remi for me because they are a lot quicker to reload with pre-loaded cylinders (i.e. Clint Eastwood in Pale Rider).
If period correct isn't a concern, I believe Uberti makes a Colt replica of the peacemaker that is cap and ball model (might not be a peacemaker but looks like it to me). Others may know more about that one.