HGST have a very good reputation and real world reliability based on read / skimming through several reports over the years of the reliability of hard drives by brand name based on enterprise usage. Meaning running 24/7 in something like a server farm. Based on the reports, a large majority of the hard drives were HGST and they had among the lowest, if the not the lowest, failure rates.
Having said that, I would have to say that I ever since I bought my first Windows PC, I have easily gone through over 30 hard drives for personal use. Only one of them actual failed (a 40GB Matrox HDD; a brand that no longer exists), and a 120GB WD which developed around 10GB of bad sectors, but no actual data was lost.
I generally replace hard drives in my desktops and laptops due to age (and fear that it could lead to failure), or I replaced lower capacity HDDs with larger capacity HDDs. I am planning on purchasing more HDDs within the next year to replace aging / smaller capacity HDDs yet again. Looking at purchasing several 8TB HDDs.
At the moment between 2 laptops, and 2 desktops as well as a few external HDDs, I am currently using 14 HDDs. I plan on replacing every single one of them over the next 3 or 4 years. Though with higher capacity HDDs, I would likely consolidate down to around 10 HDDs.