Materials Engineering is still a bit alien type of field in Pakistan... I knw its interesting and has quite developed itself but in foreign countries, for Pakistan i would recommend u Mechanical Engineering... Giki is really amazing place for Engineering... But its damn expensive ... Also u should select that field which has some job factor... Mechanical is a really broad but tough field and almost its on the top of merit in all universities of Pakistan.... So Brother i would simply recommend u to go for Mechanical....
P. S: i am also a Mechanical Engineer