It depends on the kind of rifle and the powder. If I am shooting LARGE powder charges I like a musket cap. Especially on an inline rifle. The straight ignition and the extra burst of flame from the musket cap helps to achieve a fast sure ignition.
In a traditional rifle, the simple #11 cap works fine. Normally the powder charges are not that large, its loose powder, and you are shooting moderate to light projectiles. The #11 also seems to help reduce the production of fouling and in a traditional, unlike an inline, fouling is harder to see and control. So I like to keep fouling minimal.
Both will work fine though. I have two rifles I use musket caps on, and that's because the manufacturer recommended it. I do have a number of rifles that "can" use musket cap ignition.
Also if you load with your fingers, in cold weather the musket cap is a little easier to get onto the nipple. But practice with the #11 caps and a capper and that's a mute point.