I cannot tell from the photos which it is either. In Erigeron bonariense, the tips of the bracts surrounding the flower heads have at least a few long hairs, and the fluffy part (pappus) of the mature flowers is white or pinkish. In Erigeron sumatrensis, the tips of the bracts surrounding the flower heads are hairless, and the pappus of the flowers is straw coloured or golden.