Howdy
I had your same question almost 50 years ago.
My first Cap & Ball revolver was an Uberti brass framed 44 caliber Navy. Yeah, not authentic, but I did not know that then.
A few years later, after getting lots of cap jams, I bought a EuroArms (now out of business) Remington 1858.
All the advantages of the 1858 design are valid. Solid frame, so no wedge to mess around with and stronger, because of the solid frame.
Yes, the grip shape of the 1858 Remington is different than the grip of the Colt style C&B revolvers. There is less space between the trigger guard and the grip, so with heavy recoiling cartridge loads I kept getting my knuckle whacked by the trigger guard, but that is with cartridges, and that is a different story.
The disadvantage of the 1858 Remington, only briefly touched on in this thread, is the fact that the cylinder of the 1858 Remington binds up more quickly than the cylinder of Colt style revolvers.
This is due to a design flaw which Remington later corrected with its cartridge revolvers.
Neither the Colt style C&B revolvers, nor the Remington has a bushing on the front of the cylinder. The purpose of a cylinder bushing is to prevent fouling blasted out of the barrel/cylinder gap from being deposited onto the the cylinder pin/arbor. Fouling blasted out of the b/c gap at high speed gets deposited onto the cylinder pin or arbor. As the cylinder turns, some of this fouling works its way down between the cylinder pin and the cylinder. This is the main cause of binding with Black Powder revolvers. Colt and other manufacturers solved this problem with their cartridge revolvers by adding a bushing at the front of the cylinder. The bushing shields the cylinder pin from fouling blasted out of the b/c gap.
This photo illustrates the problem. There is no bushing on the front of either the Colt or the Remington cylinder, they are both flat faced. However in my experience the Colt design will keep running longer than the Remington design without binding for two reasons. The cylinder arbor is larger in diameter on the Colt design, which spreads the fouling out over a larger surface area. Probably more important, the Colt arbor has a helical groove running around it. The purpose of the groove is to provide clearance for any fouling that has worked its way down between the arbor and the cylinder. You will notice I have cut some grooves into the cylinder pin on this Remington, in an attempt to imitate the helical groove on the Colt style revolver. The idea was to slather the grooves with Bore Butter to keep the Remington rolling longer. Because the grooves were crudely cut with a file and a drill press, because there are not very many of them, and because they are not very deep, they did not help much.
So there you have it, the old Colt vs Remington quandary. In my not so humble opinion, the Remington is a better all round design, except for the binding problem. Slathering the Remington cylinder pin with Ballistol is a good workaround. A better work around would be adding a bushing to the front of the cylinder and cutting a relief for it in the frame. Unfortunately, I don't know anybody who does that anymore.
The Ruger Old Army has been out of production for a number of years now, so they are only available used, and the price of them keeps going up.
What ever model you decide to buy, do not cheap out and buy a brass frame. The frame can stretch from heavy loads, I have experience with this. Do yourself a favor and buy a revolver with a steel frame.
Regarding target sights, I prefer my revolvers to look authentic, so I would not dream of buying a Remmie with target sights.
But that's just me.