Battle Royal is a 9 hour epic battle which is more time exceeding (depending on clan strength) and Evanescence is 5 hours I believe. Honestly, both of them are attack attack attack (for the most part). Evanescence has less total damage needed to complete than BR by far but 4 hours less time. Conclusion, if you can have 5 active hours with your clan mates, or perhaps less; it's easier. Battle royal gives you extra time to spread attacks out (not recommended) and xstal if needed.