On a form, I would like a specific report to run based on the choice made it a field above. i.e. If choice "1" is chosen in the dropdown field, the a report would display below matching a field with "1" also.
You can make a Report Link field and on the left side of the configuration have your 1 2 3 multiple choice field and on the right side match it up against the similar field on the details report.
But note that tis will only take effect once the record is saved. It will not dynamically change in edit mode. hence, I suggest that to avoid user confusion, that you only show the embedded report in View mode.