Having used Signal, Telegram, and Whatsapp heavily (friends on all three, natch), here's my one absolutely critical beef with Signal:

It doesn't always deliver messages, and it more frequently doesn't deliver them in a timely fashion.

In my experience, Signal delays delivery of messages about 5% of the time -- which is actually huge and makes it unusable for reliable chats.

The story which made me never trust Signal again: I was out of town and trying to coordinate with a backup pet sitter, because my original pet sitter became unavailable. I sent them a message via Signal (their preferred chat), heard nothing for a day, and started frantically calling around to everyone I knew who had a key to my place to please take care of a pet.

Several days later, I got a reply from them..."Hey, I just got this. Did you need me to take care of your pet?"

Over the course of several months of regular chatting with my then-significant otter, I also noticed once or twice in every two week period we'd have a half-day delay on messages...just...silence from one of us or the other, followed by, "Where were you? I texted you hours ago." from one or the other of us.

I know not everyone has these problems with Signal, but I've also seen enough other people on here alone complain about this that I know it's not just my hardware or network setup (this was across both Android and IOS devices).

For that alone, I will try to deflect away from Signal for anyone who's got any other chat methods set up.

Telegram, on the other hand, has been absolutely reliable, both in regular and secure chats. Never a lost message, never a delayed message.

Same for Whatsapp.

Signal also has the worst UI of all of them, and it comes down to all the polish that free software almost always lacks. On Signal on Android, you can select different colored themes (I like night mode for everything); on IOS, you're stuck with white. The chat bubbles are very plain on Signal, on Telegram they're a little fancier. You can set a chat background on Telegram; Signal, it's a plain white chat. Telegram? You can add sticker packs and use stickers in chats. No stickers in Signal. Attaching photos is cruder in Signal. Group chats are weirder in Signal.

If the visual flair doesn't matter to you, then fine, I get it, you don't need to tell me it's not important -- it's important to me.

And one more thing that isn't really 100% Signal's fault but absolutely drove me mad when I used it on Android as a replacement to the default SMS app: there's no real way to know when someone sets up Signal and then uninstalls it, and Signal defaults to sending secure messages every time. So, there were a few people I'd text who, I'd send them a text (which Signal sent over its own network), hear nothing for a few hours, then remember that they were one of the people who had uninstalled Signal, and I'd resend the message via non-encrypted SMS and receive an instant reply.

No way to tell Signal, "never send to these people via Signal, only use SMS with these people," which adds a tremendous friction to a chat app that really shouldn't be there. Not 100% Signal's fault (those people arguably should be "deregistering" from Signal) but absolutely within their ability to build a fix for it.