I want to preface this by saying that I use almost only signal, but I do get the appeal. Walking out of the house and switching from wifi to mobile is so smooth, signal always takes a hot minute to reconnect, but with facetime (and for that matter meet and whatsapp video calls) you barely get a stutter. For the most part it really is a "it just works" solution whereas signal sometimes feels a little klunky. I don't mind, but I get that people value that.

For messages not much reason, for video the comparison is a joke.

One major thing Signal is missing is CarPlay (and Android Auto) functionality.