I would have to vote call. I spend some time speaking with my representatives.
Anyway, with a phone call, you can introduce yourself, discuss the issue at hand, inquire as to his/her intentions on voting, find out why they are voting that way, what are their concerns with voting the other way (if you'd like them to vote the other way), etc in a flowing manner. If you e-mail of course you can ask all the same things, but you will likely get canned answers, and the dialogue won't flow like with a phone call. With a phone call, they have to answer right away. You will get more straightforward and honest answers with a call I think.