I dumped WhatsApp within a few days of when FB said they would be changing how whatsapp deals with user privacy. A lot of other people did too. I'm happily now on Telegram.

Telegram is now going to force ads and block apps that don't show them..

And their chats are not even E2E encrypted except their 'secret chats' but they work only on one device and don't work in groups.

I don't like ads either, but they're only going to be in channels, not in groups and private conversations. And if someone really wants to block ads, there are alternatives:

* Build and install a custom client with your own API key, and don't share it with anyone

* Use an Xposed module (already exists) or Cydia tweak if you're willing to root/jailbreak your phone

As for the encryption, it depends on your threat model. Yes, full E2E by default would be ideal, but even with their default cloud encryption they're probably a lot more trustable than Facebook & co. According to their FAQ, the data is scattered across servers in multiple jurdistictions, so a lot of governments would have to team up to get any data out of them.

But also, how do you handle convenient cloud backup/sync with full E2E? WhatsApp and Viber both constantly manage to lose messages for me when restoring after a device reset or switch.

Why not just use Signal instead?

Bad tools for moderating large channels, no bot support.

I don't know about the moderation tools for large channels, but bots should be possible: https://github.com/AsamK/signal-cli