In the US, of all places, is probably the safest place to run an exit node. There are organizations out there just waiting for a perfect case where someone is sued for running an exit node to prove that tor exit nodes are perfectly legal.
This is the common 'common carrier' exception. And I don't think it is unreasonable to say that the EFF, in particular, and EPIC, ACLU, etc, are in fact, said organizations. Nor would it be unreasonable to ping your interests in becoming an exit relay past them beforehand. They have publicly stated that, were an operator to be running a relay, and be having a 'clean' life upon the date of the relay's inception, they would be quite interested in evaluating any case brought against such operator. That is very laudable and one worth looking into, especially, and presumably so, if you can provide an independant corporate housing for such service.