The most accurate way to answer this question is to figure out the match percentages (# who ranked/# who matched) among DO's in the specialty of interest and compare it to that percentage among MDs. It is likely that these numbers are published somewhere (AOA website? ERAS? ACGME? Frieda?).
I think most people would say DOs have a harder time getting into competitive specialties, just by virtue of the fact that we don't see a lot of them, but, of course, we don't know whether fewer are applying/ranking, or if they really are accepted at a lower rate than MDs. And, of course, fewer may be applying due to self-selection and self-perception that their chances are lower and then going into less competitive things. And I suspect there are some subtle pressures at DO schools to go into primary care, but I guess I don't really know this.
I suppose the best advice, and this is probably also true for MDs, is to shoot the moon, but have a backup you can live with.