I've been farming story bosses primarily as they seem to have a better drop rate than Taken Champions and strike bosses for me. I farmed Primus Ta'aun and the other ultras when Regicide was the daily heroic. Nothing unusual dropped. I think I picked up No Backup Plans and an Alpha Lupi (hunter). The Gatelord on 240+ has been most generous to me. I picked up the 4th Horseman and Telesto from him. I thought about trying the Court of Oryx, but he last few times I've played, it was an over the top rapid fire Battle Royal. It's fun if there are a bunch of people doing it.