The Frame question isn't nearly as important as all the things bison referenced. A well made accuraized and tuned cap and ball revolver of either can shoot great. A sloppy action of either can shoot equally bad. More folks seem to have more problems out of the box with the Colt repros, but that isn't always the case. A crappy remington with a gritty trigger pull will be terrible. There are vastly different quality controls even off the same production line. While Jim's Discount center's may order the (wholesale price) $89.99 quality in which less attention is paid to fit and finish, Craley Hardware gun distributors may spend more like $109.99 and specify more attention to the works, trigger and smoothness of the action. Another outfit may be real sticklers and demand the best the factory can do, fit finish, actions tuned, etc at $149.99. All stamped from the same manufacturing facitlity, or perhaps contracted to have other names on them.
I have 15 or more black powder pistols, from sidelocks, flint and perc, to cap and ball of both top strap and colt types, even box lock-in line type muzzleloaders. I suspect that it is easier to shoot well with a muzzle loader pistol, but not nearly as exciting. I can shoot fairly well with my Ruger, and less well with my .36 1860 Navy, but much better with my 1862 Police model. Regardless of which, I can shoot far better with my Palmetto in line 44 caliber muzzleloader. I have an old TC Patriot and could never sight that thing in for decent accuracy. As for my Traditions Trapper pistol in flint lock, I can kindly say that sometimes it goes off. Obviously, I have favorites, especially those that shot well out of the box.
Some folks have a bit more trouble sighting along a colt repro simply because of the hammer notch being the rear sight. Like all things, it can take working up a load and getting used to it.
Some folks have personal preferences that have little to do with actual performance, sort of like a Ford, Chevy, Dodge truck preference. If you buy a quality gun, it probably won't matter which type you get. I once saw a guy shoot an incredible group with a Walker repro. About a 1 inch group at 25 yards. Then I heard that he was a skirmisher and had probably fired 10,000 shots through the thing, it was the only gun he ever used in competition and shot the thing a few hours per week and he paid some well known Pistol smith almost $1,000 to tune it and accurize it.
