Agnostic. But I don't really see a point in atheism. Most common reason I see people say "I'm a atheist" is because they consider themselves "science people". However if you are a science person you wouldn't assume either way, science isn't "there is no evidence so therefore it doesn't exist."
Another reason would be "I'm not a christian" or "The bible is bullshit". But atheism isn't the disbelief in Christianity its the disbelief in god. You can't just discredit Christianity as your reason for being a atheist, you have to discredit ALL the possibilities for a god (or gods).
Because of this atheism is just as much of a religious belief as Christianity is, which is why i'm Agnostic. If there is a god I believe he just cares that I acknowledge this, and that I practice good morals. I don't believe I need a bible or to follow some strict set of laws.
There are two definitions atheists like to throw around with no consensus to which one they're going to use.
A.) A lack of a belief in a god.
In this sense, I am an atheist. I do not believe in any gods,
B.) A believe that there are no gods.
In this sense, I am still an atheist, but this I feel no where as strong about. There is no way to prove that there are no gods, I purely believe that there are no gods based on the lack of logical sense produced by others, or by me, to suggest that it would be accurate or logical for a creator. It's entirely a belief, there's no facts to support the argument, only the logic I used to come to the conclusion. Though it's not a religion, it is not a system of beliefs.
As for people deciding for atheism over Christianity, it's ignorant to throw away Christianity and not bothering to see any of the other religions instead, but then again, often times the same reasons they decided off Christianity will fit into the other religions as well. A problem that goes to the base of all religions. Though I don't think it's good to be boistering around about how Christianity sucks. As much as I don't like it, i accept that it has helped people, lots of people, and some people need it. And if it helps ONE person, then it is a good thing. It's not religion that causes problems, it's people who use it in bad ways. So I do support most religious people, they mean good and I appreciate this. My views don't change a thing, the only person they effect is me, and who cares? There's much more pressing issues.
Edit: To be clear, I'm not trying to argue anything. I'm expressing my viewpoints whilst also trying to clear some things up.