It really depends on needs. Just about any external HD will be similar. If you want expandable...usually that means a RAID array of some sort. For backups, a single drive is easy and inexpensive, and you can run more than one and swap them on a schedule for redundancy. HDs are cheap, so I would start with something like a 4TB drive.
While nearly any brand external drive these days is fine...most are factory sealed and the enclosure can't ever be opened without voiding the warranty. Many are plastic, which is a good insulator...keeps the heat in. Aluminum cases are good sinks, and help keep the drive a bit cooler. Something
like this is a good place to start, either with a HD, or use your own.
LaCie makes nice cases, but they put a standard drive inside that they select (not the user). The LaCie big dock is TB3 which is great, but a premium cost. The ports are handy too...a drive plus a dock. The Seagate IronWolf drive is good for running continuously. The case is aluminum. This should be great for most any user, but a premium product at a premium price.
If you do want expandable, we can talk about pros and cons of RAID array with multiple bays.