I'd say Telegram is probably the "nicest" app I've used for messaging. WhatsApp and Messenger are Ok. Signal, whilst being idealistically the best, is spartan, kinda ugly, and lacks many features that make messaging "fun".
It doesn’t, you aren’t compelled to use Signal, I care that the clients I’m talking to are conform to the spec and don’t expose myself to side channel attacks (e.g. previewing content directly from the client)
Fortunately, I'm not. But due to the nature of messengers, I likely would if Signal became popular.
If you don't want others to use a client of their choice for some (real or imagined) security benefits, that's between you and them. I think most people will think your priorities are silly.
Telegram has been picking up steam in my wide network. It's been surprising to me how easy it was, as an early adopter, to convince people to use it. It doesn't work with everyone; WhatsApp dominates around here. But in the tens of people that I care to communicate with have happily switched to Telegram for much of their chatting.
It's ad free and open source.