I also dislike when mate is too bitter, but that doesn't generally depend on the yerba itself, but rather on how you prepare mate.
Try:
- removing dust from yerba, by covering the top of your cup with a slightly humid cloth and shaking it for a few seconds (the dust should stick to it, but the leaves should not)
- heating using water a tiny bit under 70 degrees hot (above this temperature the first mates will be too bitter, and the last too washy)
- pouring water always in the same place, so that the leaves slowly get wet from bottom to top
Try: - removing dust from yerba, by covering the top of your cup with a slightly humid cloth and shaking it for a few seconds (the dust should stick to it, but the leaves should not) - heating using water a tiny bit under 70 degrees hot (above this temperature the first mates will be too bitter, and the last too washy) - pouring water always in the same place, so that the leaves slowly get wet from bottom to top