The Roku 4 offers more 4K content than the Fire, but aside from that and the Sunday Ticket thing I'm not sure there's any substantial benefits to going with the Roku over the Fire.
My Roku 2 is not long for the world (I have to restart it almost daily now so it won't freeze or give me error messages) and will probably be upgrading to something newer soon. I'm not a brand loyalist, so I'll go with whatever works best.