I love many small features of Telegram.
Telegram had replies to messages before Messenger, WhatsApp, and probably other similar apps (they said they were "the first" or something). Replies in Telegram are very nice to use. In the chat view, you have this standard floating down-arrow which scrolls to the bottom of the chat when you click. When you see a message which is a reply, and you click the preview of the message that was replied to, you jump to it, and then the floating arrow won't take you to the bottom of the chat, but to the reply from which you've jumped. And it works for more than one jump, so you can kinda navigate chains of replies.
Also, jumping to even very old messages is much much faster than in the other chat apps. On the desktop client, when you scroll up there is a floating date at the top, when you click it, a calendar appears, there you can jump to any day in the chat, and again the jump feels instant, like no loading. On the Android app, clicking on the floating date jumps to the beginning of the day, but you also can access the calendar by a button that is shown when you are in search mode. By the way, searching also feels instant.
This year, they added a new mode of replying by quoting only a part of the message, so you can select some words from the message and reply to them (you can do it on mobile too). Another new mode is replying to messages from other chats, so for example you can quote and link to the message from group chat in some private chat.
I could go on and on about features like these.