If I claim that Saturn is ruled by a society of giant purple hamsters, and you disagree, who has the burden of proof, me or you?
It's obvious, isn't it?
Yes, it's obvious, the one making the definitive claim, which in this case is you claiming a hamster society on Saturn. As far as the real discussion, since it's atheism making the definitive claim there is no God, then the burden is on atheism to back up their definitive claim...very clear. So, where's your proof?