To me, as a marketer cum advertising personnel, both strive on user generated content. They are what users update, upload and share. They are what users are. They are what consumers are.
But they are different.
#1
I see a major difference while searching content. In facebook, you just can’t search for consumer content. It is all about your friend’s network, a business page and their latest updates. On the other hand, twitter sometimes is better than google in giving you consumer voice, brand information and sales message. Comments, images and short URLs are all part of the search feature. Any user could search the wide user generated content.
#2
Twitter is non-personal to a great extent frank, candid and opinionated.. The users are not bound by his friend circle to act, say or behave in a certain way. Twitter has an independent universe not limited to a set definition. Facebook on the other hand is about friends, groups and business pages. It is limited to the followers and friends.
#3
Twitter is about content, whereas Facebook is about friends
#4
Twitter is about sharing and reading anything of interest. Facebook is about networking and keeping in touch.
#5
Facebook can give instant popularity to an information in a community or within a closed group, whereas Twitter may need hard work and strategic placement. Facebook is therefore better for brand awareness, whereas Twitter is about brand engagement.