What are your typical spending patterns? The cards have different high cash back categories. You are already hitting a lot of good cash back categories with your current cards.
I'd go with the Forward as well. Like others have pointed out, you already have Discover and the Freedom. The Dividend's categories (well, IMO at least) tend to be overwhelming. This quarter (toy stores, electronics stores, and Macy's) is decent, but next quarter sucks bootyhole. 
The Forward gives you 5x per dollar spent at restaurants AND fast food, bookstores (it counts AMAZON.COM as a bookstore!!!), movies, and music stores. Pretty good categories if you ask me.