Re: Signal vs. Others
Signal is acknowledged to have the best encryption protocol, which is why it has been adopted by WhatApp, Google and others. Unfortunately, partly because of the quality of the encryption, group management has traditionally been difficult as groups are essentially a series of individual chats. This is due to change soon as a now have a way to secure accounts with even less metadata. Both articles of full of technical detail but worth reading if you're interested in the kind of problems they're looking to solve and the solutions they've come up with.
Wire is okay but suffering from having no real USP. Threema, also based in Switzerland, offers stuff for businesses.
But for basic group, particularly when you want this to be public, and chat stuff Telegram is about the best, especially as WhatsApp is soon due to start including advertising.