Both apply to me, though the first one applies more in an "I think the non-existence of gods is more reasonable than the existence of gods" sense, not in the "I am absolutely certain that no gods exist" sense.
Standards of Truth; Certain Knowledge does not exist, one must establish a standard of truth, or forever be unsure of what one believes. Certainty is a statistical term.
Standards arise from experience, one's own observations, what one is told, etc. Which experiences give repeatable results, or which beliefs do we 'like.' Consider all of this.
For me, I have reached the Standard of Truth that if it is not natural, it lacks import. If it can't be felt, then it has no feeling, if it can be seen, it has no appearance, etc. If it is not natural, then it is irrelevent, because I have no way of sensing the super-natural or even knowing if it exists.
So I have a standard of truth that tells me observation of natural phenomena is all I have to base truth on. The second standard is that if there is something supernatural it is, for all practicle purposess, meanignless.
Now, I don't believe I have 'certain knowlege' that god does not exist, but I have as close to certain knowledge as one can come that there is no reason to behave as if I believed in god. In fact, behavior, based on unreasonable claims and beliefs, is dangerous.
Behavior based on the here and now, on the human condition, can produce results. Behavior based on a belife that a supernatural being will give you 72 virgins if you blow yourself up can send planes into skyscrappers.
So my certainty, is that, whether god eists or not (a meaningless question), it is immoral to make decision or behave based on any knowlege other than here and now, natural, that which we can experience for ourselves.
I am 100% certain, that 'belief in god' is the no. 1 cause of idiocy, death, conflict, starvation, genocide, disease, etc. Whether he actually exists or not is meaningless.
Also not that is not necessarily a beliver that causes the pain. It is quite often someone who couldn't care less about god, that manipulates believers. I.e. believers are a natural resource to be used for ulterior motives.