Types of messenger

Pros:
- Solid interface
- Can be anonymous
- Easy to block annoying people
- Reliable
- Good functionality
- Free and widely available

Cons:
- Can get cluttered if chatting in big groups
- Notifications can be buggy
- Doesn't like being logged in in two places at all
- Not great at taking photos/videos directly
- Rubbish at sharing links

Alternatives:
Google Hangouts - Comes as standard on almost every Android device. Pretty decent, but needs a google account which is annoying
Snapchat - Not as great at chat, but much better at media sharing
Whatsapp - Great at chat, above all others, but sucks at media and links
Skype - Great alrounder, but on mobile is really not that good
Yahoo Messenger - Yeah, yahoo is still a thing. Same as Hangouts but needs yahoo instead of google

My preference is Kik. It does the job very well whilst having the largest user base. It's what i would recommend. That and Skype, but people understandably don't like to give out skype as it's inconvenient to have two accounts on one computer