I've declared Minimum Fuel at least once each approaching ORD and JFK. When I did so, I already had ready the responses to the inevitable ATC questions: Are you declaring an emergency? [No.] and What are your intentions? [At ttttZ, if I am not yet cleared for an approach, I will have to divert to XYZ.]
The key is to decide your options and when to exercise them BEFORE you make the declaration to ATC. Once you get to the decision point, then you can declare Emergency Fuel if necessary.