I have a Uberti 1858 in Millenium Finish. It was not expensive, and the finish is not so pretty that I'm bummed if it get scuffed a bit. The Ubertis have a dovetailed front sight, so you can tap it over to adjust POI. That's an advantage, I think.
I'll recommend the Uberti without reservation. However, I was assuming that Augustus McCrae had a gift certificate to Cabela's or something. (Did I mention that Augustus McCrae is the name of our new dog?)
I'd go with the original sights. They're absolutely fine at 50 feet. I have them.
One reason I recommend a Remington is that the sights are generally a lot better. They're usually set to shoot POA at normal pistol distances, and the rear sight is a notch on the frame like a SAA. Colts shoot very high and are very hard to adjust if they're off, and they usually are. The rear sight is on the hammer. A Remington is a very solid, simple design that's clearly the forerunner of the modern revolver. The frame is one simple part, and doesn't unscrew into a bunch of parts like the Colt.
The .36 revolvers will be a tad cheaper to shoot, since the bullets are a bit cheaper, they take less lead if you mold them yourself, and the powder charges are smaller. But they're not man-stoppers. They work on rabbits, though. If you want to hunt something bigger or have the gun as a self-defense gun in any way, get the .44.
I would not recommend a Walker as a first gun, though they're neat. They're very, very heavy and the loading lever is problematic. They have the same sighting issues as other Colts. Replicas are also expensive.
I think a Remington NMA .44 is a great first BP gun, though I'm prejudiced, since it was my first BP revolver. When the old one got tired (early '80s low-end Italian gun with soft parts), I replaced it with another, this time a Uberti 1858. So I must have liked it.
Another cool choice is a Rogers and Spencer from EuroArms. It's top-quality and a great shooter.
http://www.dixiegunworks.com/
http://www.buffaloarms.com/
http://www.texasjacks.com/ sometimes has good sales
Note that various manufacturers do vary in quality. It's often worth paying an extra $50. Uberti has been consistently good, though word is Pietta is good now, too. I looked for Uberti, myself, since I wanted to be sure my new gun would be a lot better than what it replaced.