Investigation by investigative journalism outlet IStories (EN version by OCCRP) shows that Telegram uses a single, FSB-linked company as their infrastructure provider globally.
Telegram’s MTProto protocol also requires a cleartext identifier to be prepended to all client-server messages.
Combined, these two choices by Telegram make it into a surveillance tool.
I am quoted in the IStories story. I also did packet captures, and I dive into the nitty-gritty technical details on my blog.
Packet captures and MTProto deobfuscation library I wrote linked therein so that others can retrace my steps and check my work.
For the internet messenger functionality that would be Signal.
For other things (channels, mostly), anything that does not pretend to be end-to-end encrypted when it is not. A website with an RSS feed would be one trivial choice for channels that are open to anyone. Public communication like that has no business going through “platforms”.