Hey filteredsoul! Welcome to the Chicago Style forum.
When I used pre-shredded, some brands are better than others, but one thing I do with all of them is to toss them vigorously in a strainer, to get rid of all the potato starch or other powder adulterants used to keep the cheese from sticking.
But you'll do better buying a block and shredding it yourself, generally. I do one or the other or even a mix of wm and part-skim for thin. I've never had a problem with part-skim. If you are going to shred it yourself, put it in the freezer for a little while beforehand, to help firm it up a little, which makes it shred much better.
Really, just keep experimenting until you find what works best for your local conditions. It'll all work out fine.