Go with No. 10 caps.
I use both Remington and CCI No. 10 caps in my Colt 1851 Navy 2nd generation (circa 1981) and my Uberti Remington 1858.
I can't tell any difference between the CCI or Remington caps in ignition, but the Remingtons seem to fit better on the nipples of these two revolvers.
Nothing is gained by using Magnum No. 11 caps in a cap and ball revolver. I know, I've tried them myself.
Because cap and ball revolvers use so little powder, compared to a rifle, regular caps ignite the powder just fine. Magnum caps are a waste of money.
But see for yourself.
Fire the regular caps without loading the cylinder, and listen to their report.
Then fire the Magnum caps. You will notice a different report but it isn't any louder, as you think a Magnum might be.
The Magnum caps sound different --- perhaps they differ in the number of microseconds in which they burn --- but they don't offer any advantage.
But you'll usually pay more for them, to pay for that "Magnum" name.
If you use the larger No. 11 caps, the lives one will fall off easier during handling and recoil, by virtue of their being slightly larger.
Use No. 10 and pinch the cap into a slightly elliptical shape. This will help it cling to the nipple and prevent its falling off.
Also, loose caps on a cap and ball revolver can cause multiple discharges. The recoil of the revolver tosses off a cap on a live chamber. Then, the flame from the cap that your hammer hit flashes over to the uncovered nipple, causing a second chamber to discharge.
I've been shooting cap and ball revolver since about 1970.
I once believed, as the manuals preach, that not putting lubricant over the ball leads to multiple discharges.
Now, I no longer believe it. I just don't see how the flame can get past a properly sized ball, tight in the chamber.
Instead, I believe that multiple discharges are caused by the flame of one cap crossing over to other caps loosened or ejected by recoil. To me, this makes much more sense.
Anway, use No. 10 caps as the manufacturer recommends. Buy a tin each of Remington, CCI and RWS (if you can find them; I rarely see RWS caps anymore).
Try them on your Ruger. Either cap has plenty of power to ignite any black powder or Pyrodex charge you put in that revolver.
If you don't believe it, load the cylinder with caps (no powder or ball) and fire it in the dark sometime.
It's an education in just how much flame those little devils produce!