I would advise against old USB 2.0 drives for performance. ;)
More seriously, any brand will work. Seagate, Toshiba, etc. Just avoid models with fancy zizmos like finger print authenticators and ignore any special software the manufacturer tries to suggest. You'll be reformatting the drive anyway and letting MacOS TimeMachine software handle the backup process.
A good rule of thumb is at least 2x the size of the drive being backed up (or at least 3x the size of the data if the drive is or is likely to become mostly full). 5TB should be good enough to backup a 2TB drive. If you are backing up 1TB or less I'd even call it overkill.