Facebook is very popular with everyone because people love to share and post pictures of events and things they are doing in their lives. You can chat with your friend, talk with them live, see what they are doing, and meet people from around the world.
Where Twitter is basically used for announcements and short messages. Even though Twitter has increased the characters of the tweet you can make it isn't personal. People basically share links and videos on Twitter. The site was designed for people to give up to the minute updates on events, what is happening, and if there is an accident to warn people of the mess on the road so they can avoid this. Furthermore, many companies use this to advertise sales, special events, and promotions. It is more of a quick message board and not so much a place to share all your photos and stuff on.
So if you are looking for a social media account that you can post images, events, or updates then you should use Facebook. If you have a quick update of an important event or an event that is taking place right now then use Twitter.