It is good that you checked the bowl to make sure it’s clear. Now snake the drain line and vent. I guess you said you did that…If the bowl flushes well with a pail of water dumped in, then you may not be delivering enough water from the tank when you flush the bowl. Make sure that your tank fills up to the water fill line (by adjusting the float valve) and make sure your tank flapper/ball valve stays open long enough to run a good flush volume from the tank through the bowl. If evefrything is as it should be, your toilet should flush fine.