If you got a white pad and no other pad with the
UDM and/or you didn't get a package deal, it's NOT the swirl buster pad. The white standard pad is a light polishing pad. It's pretty much an all-around pad that's not excellent in any one thing.
I would use the 5" pads. They're easier to center on the stock backing plate and you get more correction out of them without being too aggressive. For spreading stuff like wax, they're not too small. It's really a preference thing though since you can obviously cover more area at once with a larger pad. I honestly don't think that 1" extra is worth the hassle and the correction power deficit (which really isn't all that much anyway.)