diet is FAR better for fat loss. read up on carb backloading and intermittent fasting. pick one, follow it exactly.
as for your question, its splitting hairs for most people. do cardio to make you better conditioned for your weight lifting. in other words dont do long slow cardio, do something specifically to help your weight lifting using similar work/rest periods. and hit your weights harder.
work hard, eat hard, sleep hard and you will get stronger with a great side effect of bigger muscles and less bodyfat.