I personally like Ashes of Love much more than Eternal Love.
I'm a huge fan of historical dramas that involve gods, magic, etc. For me Ashes of Love gave me everything I wanted in a historical drama, great villains, slow burn romance, heartbreak, a naive FL who later becomes stronger, and a story that kept me hooked until the end due to all the twists and turns! Also, as a fan of intense love triangles, I love the two triangles that were shown throughout the story!
On the other hand, I do still hold Eternal Love close to my heart and I do think it is much better than some historical dramas that have been released lately. I loved how strong the FL was, she didn't need the ML's support often(Well, when she had her memories lol). What I also liked about this drama was the secondary couples! (Especially Dong Hua and Feng Jiu :)), they were so adorable and helped me carry on watching.
In conclusion, I think these two dramas are very similar in terms of their production (CGI, Costumes, etc) and most definitely their memorable OSTs! But personally, Ashes of Love gave me more satisfaction because of it's plot (Slow paced romance, villains, love triangle, etc).