(ぎろん) A regular argument – “That movie was rad!” “No, it sucked!” Or when Fox news and MSNBC argue.   $$$
(ろんそう) An ongoing intellectual war that can last years – for instance the debate between String Theory and the Standard Model. Or between Creationism and Reality.
(とうろん) Less antagonistic than the other two. Also, 討論 involves more than two sides. It’s more like a round-table debate.