In my opinion, Planetary is better for its damage buff. However, if your Sparkle has trouble to reach the 160 breakpoint, you can equip DDD on TY and use her ult after Sparkle's skill to maximize the advance forward. DDD would be better only when you know what you're doing with the advance forward. Also, if you run that party for Pure Fiction, I would prefer DDD over Planetary.
No worries, I'm glad to answer questions about HSR. If you have any other 5-star sustain, they are good as a replacement. However, if you don't have them, then sustains with cleanse like Gallagher, Lynx, or Nata are also great. In my opinion, E2+ Gallagher might be the best 4-star sustain right now, but March 7th can also be a great replacement and works really well with her FuA and freeze on ult if you pair her with Robin and Ratio. Hope my opinion helps :3
