If you only need the one channel and you need to manage a 100+ people, Telegram is by far the best tool. For "communities" Discord is a bit better, since you can split stuff to multiple channels. Anyone with basic knowledge of the internet can also install bots on both to manage dozens of different things.
Signal on the other hand is SUPER SECURE (although you will be giving your phone number to everyone), but no bots and no real ways to manage hundreds of possibly unruly people on a single channel.