You can't compare suffering, and so I don't think there is a valid answer as to who suffers the "most." Personally, gender is very important to me, however from the other angle--throughout history males have been brutalized, discriminated against, treated as disposable by society, jammed into restrictive cruel gender roles, and subjected to extreme amounts of violence--this continues into modern times. I also find children's rights and GLBT issues very important; and I respect people who are interested in linking up issues and struggles instead of just dividing into "most important" camps.
That of the 'traveler' also greatly incites me--in the various places I've lived in the U.S, there has always been so much discrimination, tension, and hate regarding who is supposedly "from here" (and thus belongs here) or not, but regardless I wasn't rewarded that label even in the place I was born--for one reason or another (my sexuality, the fact that I didn't conform to gender roles, my age, my interests...)