Looking at WD My Cloud EX2 Ultra 2-Bay Diskless Network Attached Storage (NAS).
Looking at WD My Cloud EX2 Ultra 2-Bay Diskless Network Attached Storage (NAS). What 2TB drives are best to install in this unit?
Or, is there an option to purchase the WD My Cloud EX2 Ultra with 2 TB WD Red drives installed?

Answers
WD Red or Seagate Ironwolf drives are the standard in NAS drives. If you're looking for file storage and sharing then 5400 RPM drives should be fine. If you're looking to spend more money then the 7200 RPM variants are nice for streaming and media.