What is more secure: Tails or Subgraph?
(Subgraph has a live CD/USB option making it like Tails)
Subgraph is definitely more secure, it uses grsec/pax to harden against memory corruption exploits and a sandboxing system called
oz to isolate and restrict applications run under it, to reduce the impact of any successful exploits.
Specifically it is intended to be secure against a remote attacker, I.E. someone trying to exploit your browser, chat messenger or document reader, etc.
The Subgraph liveboot option will not be as comfortable or kept up to date with security patches, which Tails is. From previous discussions with the developers they don't (currently) intend to make a liveboot distribution. You'd be best served installing it, not running it in a liveboot mode.