Without knowing why you want to do a politically related internship, it is difficult to make a recommendation.
For example: If you have a desire to run for political office, then it may be wiser to work at the party HQ rather than for a specific politician–unless that politician is very powerful & influential.
Specifics matter. Does the US Representative face primary opposition ? If so, then this may not be a wise choice for one intending to run for office in the future.
Also, interning for a US Senator can be quite different than interning for a US Representative. Broadly speaking, interning for a US Senator is more prestigious, but not in all cases.