More accurate? Well... That's hard to determine. They can all be accurate. The 5R's benefits are in the design of the rifling. The design of 5R rifling has offset lands & grooves which causes less bullet deformation, which is supposed to lead to more accuracy from a less deformed bullet with equally applied pressure as it travels down the bore. The edges of the rifling are rounded and at lower angles than standard rifling, which will lead to less copper stripping from the jacket and building up in the rifling. So it allows more shots between cleanings, and less copper fouling, and copper buildup. It's design also makes cleanup very easy and quick.
I have rifles with all types of rifling, and many with 5R rifling, and there is a noticeable difference in shot-strings between cleanings, and also how quickly and easily it cleans up compared to standard rifling.
This is my experiences with it.
Polygonal rifling is mostly found in large-bore rifles and .45 ACP pistols. Occasionally you'll find it other calibers. All of my pistols with polygonal rifling are very accurate, but I'm honestly not sure if that has anything to do with the rifling.