But realistically, if it is never unplugged and only used read-only as a media source, it's unlikely either will fail in a couple years at least (probably longer). If it fails, just buy another to replace it.
This is just playing media back, right? Keep a copy of the media elsewhere (and, if it's important to you, check that you can access it periodically) and buy the cheapest thing you can find for the TV.
That’s not necessarily true. It all depends on the flash and controller used in the USB drive. There ARE USB drives that are specifically designed for high endurance.
I have a USB stick that’s literally using an SSD controller internally and SSD quality flash. It’s much more expensive than a normal USB drive.
I would also argue that (micro)SD cards have very poor write endurance due to a lack of an internal controller.
I believe (micro)SD cards actually do have a controller. It's also possible to "Trim" SD cards via MMC commands, though this requires them to be accessible directly (i.e. /dev/mmcblk on Linux).
If you need USB-based storage that should be performant and reliable, there is a no-brainer solution: NVMe enclosure with a medium to high tier SSD. It's really hard to match the speed, reliability, and price of this solution.
Neither. I had photos (long since transferred) taken onto an SD card. I recently looked at them after a couple of years to find many of them corrupt. Same for unused usb drives. You need to mount them periodically.