It doesn't matter if you buy an external HDD from one of the companies that don't make HDD's, they will be using a HDD made by either WD, Seagate / Maxtor (Seagate now own Maxtor, Samsung or Hitachi.
Here is my experience of these HDD manufacturers over the last 15 - 20 years or so.
I also work for a small IT company and we sell bucket loads of HDD's and also use them in our bespoke PC's.
Maxtor - years back they had a major problem with bad sectors with their HDD's and within the IT industry, they were heavily scorned.
We used them at work in the Majority of our PC's for about 4 years and they were very reliable.
About 18 months ago we stopped using them because we notice reliability issues and switched to Seagate.
Seagate - while they tend to be noisy I quite like them and reliabilty has been good for us at work.
Western Digital - Their QA can be a bit hit and miss. We tried using them at work but got fed up with constant new stock being fautly.
Hitachi - They took over IMB's HDD division when IBM pulled out of the market.
IBM Deskstar HDD's earned the nicknamed 'deathstar' because of major issues with their drives.
Hitachi still call them Deskstar and although they are far better than when under the reins of IBM, their QA can also be a bit hit and miss.
Samsung, for years we've used their optical drives and work and they've been extremely reliable.
A few years ago we tried their HDD's but had too many reliability issues.
About 18 months ago, I started putting together PC specifications for computer magazine reviews and we continue to do well with 'best buy' awards.
My boss wanted to keep the costs down in some areas so we could improve in other (graphics card for example).
He insisted we used Samsung HDD's because of the price and they were getting very good reviews.
Thankfully they've been very reliable for us and I also use a pair in my main PC.
Obviously this is just me and my colleagues experience and plenty of others may disagree.
Personally, if I was in the market for an external HDD, I would opt for one that uses either a Seagate or Samsung HDD.