I like and I use both of them.
Both are peer to peer but Keet is completely peer to peer so a bit more difficult to implement for the developers and to make it work on every networks while SimpleX has some dumb servers to relay messages to users so technically not completely peer to peer.
SimpleX has the option to create a new random account every time you connect to a new person.
Keet alpha had a lot of issues when connecting with people under networks that are not P2P friendly, but the new Keet beta (v.2) works very well and I’m using it daily also for my calls on my laptop!
Privacy wise, they are both E2EE. SimpleX servers can see your IP address while the person you are chatting with on Keet, that is purely P2P, can technically see your IP. In both cases, better to use a VPN.
SimpleX has the option to be used with Tor and also has the option for disappearing messages after a certain amount of time.
Many new features are coming on Keet in the next weeks.
Finally, Keet is not yet open source but it will be on February 2024 when the developers will also present and make open source the entire Holepunch 🕳️ 🥊 platform (the one used also for Keet) to easily develop fully peer to peer applications! They have the claim that Holepunch can make everything peer to peer.
Hope this helps a bit! 💜
Let me know if you want to connect with me on Keet or SimpleX! 😉