When comparing Tails vs Slax, the Slant community recommends Tails for most people. In the question“What are the best Linux distributions for desktops?” Tails is ranked 18th while Slax is ranked 33rd.
Ranked in these QuestionsQuestion Ranking
Pro Privacy focused
Pro Has TOR built-in
Use the Internet anonymously and circumvent censorship; all connections to the Internet are forced to go through the Tor network.
Pro Persistent changes
Changes you make in the configuration persist if you run from USB.
Standard tar archives plus some simple shell scripting produces modules that you can load dynamically into the OS for added apps and functionality.
Pro Modern desktop
Pro Small footprint
About 200mb, but with a full KDE4 environment and loads of useful apps.
Con Not for daily use
Tails is a privacy focused Linux distro. The updates that you will receive are only for improving privacy and not for improving user experience.
Con Saved states are not present for security
For security reasons, saved states are not supported in Tails. Files can be stored in a separate, persistent volume which must be accessed with a root password. Personal settings (e.g. -- keyboard layout, window settings, etc.) are not saved persistently across reboots. This can be a hindrance for anyone not using English as their language, or not using a QWERTY keyboard layout.
Con You can't install it to a hard drive
Con Slow internet
Tails uses the TOR network and as a result the internet on your computer will be very slow.
Con Works slowly on old computers
Con Infrequent releases
Since Slax is maintained by only one person, releases are not that frequent. So it may take a while to get bug fixes or new features once you start using it.