A tale of two sides. About ten years ago CCI got a bad rap because their six-sided caps represented a fragmentation hazard for file partners firing in close formation. Civil War reenactment events subsequently banned their use for safety reasons. Some years later CCI made a four sided musket cap, in copper instead of brass which is the material they were made from in the 1860s. These were made specifically for Civil War muskets. For whatever reason, although the CCI copper musket caps were a fine product they never really took off with reenactors. Probably because of the problems with the earlier six-sided caps not being permitted at Civil War reenactments, which is where they were most often used. Who knows? All I can say is there were/are no known issues with the copper 4-wing CCI caps.
The RWS are probably the most popular and have always been reliable percussion caps. A new brand is being offered by the German gunpowder firm Schuetzen. I picked up 1000 of them to try out and they are (like all Schuetzen products) excellent as well. They remind me (except for packaging) of the old Navy Arms caps that came in the 250 count tins with the yellow priming charge, except these are orange. They all cost about the same except CCI is about ten dollars less per thousand.