Pond 5 is without any question one of the best agencies to sell video footage. They are innovative and have an interesting earning system, where you can set the price for your work yourself. Every clip from HD to 4k will sell well and pay off nicely!
Dreamstime is one of my favorite Microstock Agencies. Their website takes a little longer to get used to and tend to refuse all vector illustrations they think are too simple, but you'll regularly sell your images here and often Dreamstime Portfolios have the best Google Ranking.
The Microstock Guide 