Notices

Telegram has been criticized for its encryption algorithms but it's not completely accurate that conversations are sent unencrypted. Client-server encryption is applied by default and end-to-end encryption is optionally enabled in secret chats, at least according to their FAQ. Also I never needed official Android client to register some months ago, I don't know if this is true now.
Signal on the other hand applies end-to-end encryption by default and its protocol is considered very good but its Android client depends on Google APIs. Plus I don't want to use Chrome just to be able to have Signal on the desktop.
I looked into all this during my summer vacation and I'm still undecided.. I'd even give XMPP a try after reading this but almost none of my friends use it

Well, yes, but I think this is a given for any messenger out there now. At least I hope there is nothing that's actually used by people but doesn't use a TLS connection.

As far as i know , you dont need an android client to register. You can just use your browser. Take the web.telegram in browser and you are good to go. And it doesnt need a plugin or a specific browser. Even N900 browser will be able to do it. I personally repect the providers who give a web interface alternative to their applications. If you dont have time to develop clients for all the different oses out there , give a good web interface. It is as universal as it can get.