They are both profitable to mine, but asic ( algorithm specific) can mine only one algorithm, meaning you cant switch bitcoin asic to Ether, and mine them. With GPUs you can switch them to any algorithm and mine all coins, but you will not be profitable on coins which have asics developed for them. Also asics are upgraded all the time and then your old asic is not worth as much. I prefer GPUs, but it is me, somebody likes asic better