For the beginner, I used to suggest the Colt 1851 or 1861 Navy, in .36 caliber.
Currently, I lean more toward the Remington 1858 Army in .44 caliber for the beginner.
Here's why:
The .36 calibers I own produce better accuracy with a ball .380 inch in diameter. Unfortunately, neither Speer or Hornady produce that ball size. They produce only the .375 inch ball for the .36 cap and ball and leave it at that.
Yet, those two companies produce three different sized balls for the .44 caliber: 451, .454 and .457 inch. Contrary to what the black books say, I do not suggest using the .451 inch ball. Use the .454 inch instead.
The larger balls, in my experience, produce better accuracy. Plus, they seal better in the chamber and discourage ball movement during heavy recoil --- the gun's not yours
The Remington has a better sight picture than the Colt, which encourages hits. The Colt design is better balanced but has only a notch in the hammer for a rear sight and a brass bead for a front sight.
The Remington has fewer parts but doesn't strip down as easily as the Colt.
More than anything, you should be asking whether you have the time and discipline to clean a cap and ball revolver after each use. You cannot just let it sit with the idea of getting to it next week. In very humid areas, such as New Orleans or Seattle, you'll likely find rust spots on it the day after shooting.
As for maker, I'd suggest an Uberti, followed by Pietta. If price is no object, and you want a Colt, get a 2nd generation Colt. This series is noted for its workmanship; the Colt Signature series is of lesser quality so I'd suggest you get an Uberti over a Colt Signature Series.
There was a time when Pietta made clunkers but for the past few years its guns have increased markedly in quality. Not up there with Uberti but some I've seen are very near Uberti and half the price.
The Colts and Ubertis tend to have deeper rifling, which helps to shrug off fouling. The Pietta rifling is shallower and accuracy will suffer as the fouling builds.
If it were me, I'd go quality the first time --- Uberti or 2nd generation Colt --- and take good care of it.
Search this website for posts by me concering how to properly use the cap and ball revolver and other topics. You'll find a lot of information in there that is helpful to a beginner.