Can anyone tell me which is more secure and why?
Trezor hardware wallet or Tails live booted from verified DVD using Electrum
Security from tails depends on how you will store your private keys. It won't be very different from using a wallet without Tails.
Hardware wallets main advantage is that private keys never leave the device and are really hard to extract.
...and to add onto that, hardware wallets are a lot easier to use than alternate cold storage methods. Rather than boot from a DVD into Tails, you just need to plug in your Trezor, open your wallet and send your funds. It doesn't get much easier than that.
I'd say as long as you safely secure your private keys (ex. memorize your Electrum seed, keep the seed written somewhere secure), using Tails + Electrum would be as secure as a Trezor. The main difference between Tails + Electrum and a Trezor is the cost - if you're planning on storing a large amount of bitcoin in your wallet, and you're willing to shell out $100 for a hardware wallet, I'd recommend the Trezor. However, if you aren't storing large amounts, or you don't want to spend $100 on a hardware wallet, then Tails + Electrum should serve your needs just fine.
