It varies upon your usage. On most Textile printing the medium hardness (70-75 Duro) is what you need. If you need to print on some signs or sticker, use hardest (85-90 Duro) squeegee. The softest (60-65 Duro) will be use to print white color on black shirts but it is optional.
If you have an automatic screen printing machine, we are recommend to use Triple Duro squeegee. it will provide more even pressure for the whole print with more critical details.