Do you have direct admit to BME at UT Austin?
If so, it comes down to what major you most want…BME vs something like biomolecular/biomaterials/biomechanics at JHU, since BME is off the table.
Have you visited both campuses? What are your career goals?
I also agree with collegemom about the money…if JHU requires any loans beyond the $27K max student undergrad loans UT Austin likely makes more sense.