I like to add molly fish with barbs. Platies suppose to go well with barbs too, but the barbs are very active, and platies feel overwhelmed by the barbs to the point where I have seen platies getting mad at barbs. That haven’t happened with gold barbs and mollies. Molly goes well with swordtail, tetras.
Mollies are more docile than platies, and mollies are bigger in size(maybe is because I haven’t seen an aggressive molly yet).
So as an all rounder community fish from the livebearers. I would say Molly!.