My favourite chat messenger is always going to be Facebook chat messenger. It's the first social media I used (Facebook) and it's why I fell in love with the chat messenger.
2go used to be my favourite chat messenger. It's a very popular chat messenger some years ago in most African countries. I don't use it again because all of my chat buddies have moved to using Discord.
Facebook messenger is my favorite because it is linked to Facebook where I have so many friends. I don't even need to download the Facebook messenger to actually chat with those my friends on Facebook.
WhatsApp is my favourite chat messenger. I haven't used any chat messenger that's better than WhatsApp in any way. It's more personalised and fully end to end encrypted chats.