When it comes to hardware ... especially spinning platter drives, there really is no perfect option. No matter what the brand or the vendor they are purchased from you can usually hear equally representative horror and success stories.
That said, I have been a very happy OWC customer for nearly 25 years ... best customer service and support available for hardware issues.
I have had many external peripherals made/sold by OWC over the years. The units start out as main working drives, then continue on as backup units as technology advances.
I don't yet have any of the Thunderbay 4 units, but have been using the Elite Pro Duals for a while. Very dependable and solidly built ... my backup units are a pair of the older Mercury Elite Pro Qx2 (four bay in RAID 5 with built in hardware controller) connected via eSATA to LacCie eSATA to Thunderbolt hub. ... again, very solid and dependable.
As for bare drives, I have had really good fortune with the Toshiba 3TB and 2TB drives ... I buy them from either OWC or Newegg, whichever has the current lowest price ... Newegg has periodic special pricing with free shipping that is just too hard to pass up.
The Toshiba drives are formerly Hitachi, which was formerly IBM and thus far, I have had zero failure with any of them. YMMV of course ... just sharing my good fortune ...
While I have used Caldigit's external enclosures in the past withou a problem, I've never used their Thunderbolt products.
I've been using the Promise Pegasus R4 for over 3 years now. It is rock solid. It comes pre striped as RAID 5. IMHO the extra initial cost is totally worth for the performance and reliability.
If you purchase the Thunderbay, be advised that the raid 5 config won't work if you provide your own drives. I was considering it, but found out that the Raid 5 option is not available if you provision the chassis yourself. I own 3 Pegasus2 units and they have performed flawlessly. I even transport them regularly to the shoot for the DIT to transfer to (along with a backup of course) and have had no issues whatsoever.