Unless you're basically a serious data hoarder or otherwise have unusual storage requirements, an 18TB drive (or maybe 2) get you a lot of the way to handling most normal home requirements.
Personally, I buy the drives with the best $/storage ratio. Right now that seems to be ~3-6TB drives. Many PC enclosures and motherboards can fit 8-12 drives, fill it up with the cheapest stuff you're willing to spend money on. It will probably break even or be cheaper than the larger drives.
It depends on the use case. As with CPUs, I tend not to buy the top-end but it may make sense to just buy for expansion over time. I think my RAID-1 Synology drives are 8TB. But mostly just use external enclosures these days anyway. Pretty much don't build PCs any longer.
AFAIK someone on reddit did the math and the break-even for tapes is between 50TB to 100TB. Any less and it's cheaper to get a bunch of hard drives.