In the realm of spiritual beliefs and using Theists, Agnostics and Atheists to represent those who believe, those who are on the fence and those who don't believe, respectively, Agnostics are correct, scientifically speaking and based on present day knowledge.
Theists say, "Look at the planets, the moon, the stars, the universe. What more do you need to prove there is a God?" Atheists say, "The planets, the moon, the stars and the universe were all created by pure chance.
Neither belief can be proven scientifically. So the only logical position to take about the existence of a god is one that discounts neither theism nor atheism nor accepts one over the other or either at all.
Is there a god? Maybe or maybe not. You can believe there is or you can believe there isn't but neither belief changes the fact you can't prove either. Maybe someday we will know, maybe not. So, from a scientific standpoint, agnostic is the correct stand to take on the age old question, "Is there a God?"