I use the very fast
SABRENT Rocket XTRM Thunderbolt Drives for my Time Machine and one-off backups/data transfers, but they've been in and out of stock for a while on Amazon. The 2TB is very overpriced right now, I wouldn't buy - I paid less than $300 a couple of years ago. The price should be going down, so perhaps it's a stock issue, or Sabrent is about to release updated models.
I also just picked up the
SAMSUNG T7 Shield 4TB which is at an all-time low price (for a 4TB drive). Not as fast as the Thunderbolt drive, but huge capacity and speedy enough for mass backups - it also has a nice soft rugged coating. Very durable. I consolidated all other random data/backup SSDs into this one.