Jeff Geerling has some great and very detailed write ups on this.

To quote directly from his post: "The results really speak for themselves. For sequential operations, using a USB SSD is 3-4x faster than using a microSD card."[0]

[0] - https://www.jeffgeerling.com/blog/2020/im-booting-my-raspber... [1] - https://www.jeffgeerling.com/blog/2020/fastest-usb-storage-o...