First of all, most of them go for the " Omnipotent, Omniscient, Omnibenevolent." I argue that, as the world contains evil, there can be no all-powerful, all-seeing, and all-loving god, because why let a creature make mistakes, hurting itself, when you have the power to always help it whenever it needs, the moment it needs it? Letting it learn for itself, while it may seem better, creates far more net suffering. Thus, God or whoever else is lacking in one of these qualities.
Another thing is, if there is some omnipotent deity, what's to keep him from getting bored and swatting us like collective flies? Gods have no reason to be nice- The only reason we ever act kind is because we have a society that imposes these morals, because we know that if we do not follow them we will be in personal danger. A god, particularly an omnipotent one, would be the equivelant of a spoiled brat with the command of the entire world upon them.
The whole tihng doesn't work for me. My parents are both technically catholic, but they both found themselves unable to believe in Catholic religion as much as they grew older. My father became a man of science in the most intense way- He's easily the most atheistic man I have ever met, fully satisfied with living a single life as long as he has left a decent son behind, and feels he's made the world a bit better. My mother, on the other hand, is a very spiritual person, but chooses to believe that anything can be, not simply in a single religion.
I'm a tad conflicted, but...
Why do you believe in a monotheistic religion? Or not, as the case may be?