According to diskprices.com, the WD externals for shucking have extraordinary value as usual if you're going mid-high capacity.
Toshiba drives are still my favorite if the prices are good - they are reliability champs on the backblaze blogs, and have no issues getting recognized on hardware (compared to the Seagate EXOS Drives). These days high capacity EXOS are dirt cheap though!
Too bad cheap SMR drives are uncommon - they are truly ideal drives for unraid.
You gotten your chassis yet? I have a very new Silverstone CS380 collecting dust right now