Whatever your most important issue, it will get no love as long as Congress remains broken. If you care about any issue in the US, you should care about fixing Congress.
I like this TED talk by Lawrence Lessig. It explains how Congress is broken and what we should be doing about it.
Lawrence Lessig: We the People, and the Republic we must reclaim
http://www.ted.com/talks/lawrence_lessig_we_the_people_and_the_republic_we_must_reclaim.html