Adding to current My Cloud Home

I currently have a WD My Cloud 3TB
Im wanting to add an hard drive to it as i’m close to reaching full usage on the storage.
Im unsure which to use/be better to use between a portable hard drive such as the external portable drive: My PassPort 4TB or the desktop drive: Elements 4TB Desktop External Hard Drive
I was unsure whether my the elements one being a desktop drive would it have faster speeds? therefore making it better to add to my NAS