First off, if you are going to use a metal hard material ram rod then do use a bushing, most muzzleloaders that lose the ability to group good lose it because of ramrod wear at the end of the barrel, I lost count years ago of how many I have cut off and rebuttoned.
Second, it may depend on what you are using it for a bushing with a stainless rod is excellant for the range but an alumium will work out better for hunting[lighter and will stay in the gun better and less chance of barrel damage when in a hurry reloading. Lee