Default Samsung 64gb micro sd

I just got my Samsung 64 gb class 10 card and having an issue with it . I've tried formatting on the phone and as fat32 on my pc and having the same issues. It's taking forever to copy my backup files from my pc to the card and when it's done, some filesjust ddisappear. Am I doing something wrong or could it be a bad card? What should it be formatted as? Thanks