DVD

• DVDs are read-only so your Tails can't be altered by a virus or an attacker.
• DVDs are cheap but you will need to burn a new DVD each time you update your version of Tails.
• You could also use a DVD-RW but those are not read-only.

USB stick or SD card

• An attacker with physical access to your device or through a virus could alter your Tails.
• USB sticks and SD cards can be upgraded to future versions of Tails.
• You can use persistence and store your documents and configuration in an encrypted persistent volume on the same device.
• USB sticks and SD cards are smaller to fit in your pocket.
• Some older computers might not be able to start from a USB stick or SD card.
• Some USB sticks, SD cards, or SD card adapters have a read-only switch that can prevent your Tails from being altered, but be aware that this protection is most probably not ensured by the device itself: do not rely on untrusted computers to respect this feature.