I like Tails. I think it’s great software, and a great introduction to Tor/OPSEC for the masses. It’s free software, debian-based, well supported and has a lot of ready-to-use utilities. It’s much better than your typical Windows 10 or macOS user running Tor Browser.
But let’s be real: by design, Whonix is much more secure. Any “simple” root exploit in Tails will immediately expose your real public IP address. Something as basic as this for instance (once the attacker has root rights):
service ferm stop && iptables -F && echo nameserver $(traceroute 8.8.8.8 | awk '{print $2}' | head -3 | tail -1) > /etc/resolv.conf && curl ipinfo.io
Whereas in Whonix, there is no way such a thing could happen. An infected Workstation could never reveal its true IP address, at least there are no known exploits to achieve that.
Regarding persistence/amnesia, it is trivial to erase the VM and clone or reimport a new VM for each new session, it is just a matter of a few minutes. It’s not a big deal. Moreover, you can keep an always up-to-date pair of Whonix VM and just clone them for each new session. With Tails, you are stuck with the version you have until a new release.
As for the sensitive files stored in the Workstation, nothing stops you from keeping them in another offline VM (be it in Qubes or with VirtualBox/KVM), even in an encrypted container, and copy-paste the important stuff when you need it (such as passwords, logins). Same thing with PGP: if you fear for the integrity of your private keys, run the encryption/decryption stuff in an offline VM. Don’t do it on your connected Workstation. Likewise, BTC transactions can be signed offline and broadcast on the Workstation with the public keys. I think it is good practice to never store sensitive files in a connected device/VM, even if it is (pseudo)anonymous.
I don’t see how it could be otherwise?
In my opinion, the biggest threat to Whonix users is the integrity of the host system. If it is compromised/spied on/keylogged, then it is basically game over. But if your host is a dedicated Linux OS (let’s say debian) on an encrypted USB key with the minimal number of software possible, never do anything else than using the virtualization software, etc., I would say it’s pretty safe.