I'm not an expert, and I don't have a strong opinion on the topic, but I use both.

Signal is good for onboarding normies to secure chat. It's easy to set up and use. A few easy changes in the settings reduce my main concerns over phone numbers and privacy issues. And, normies have probably heard about it.

I like SimpleX. I think one thing that attracts me to it from a secuity standpoint is you can run your own server. Unfortunately, the only "easy" way I know to do this requires ToR, which excludes all normies and probably myself, as Orbot tanks my phone battery.