I believe in a Haruhist god because well, If I think about it, the thing about God making us humans for a certain reason doesn't quite fit, he's dead now, and I don't think anything we achive physically will affect "Heaven", nor do I believe in Heaven.
As for Buddhism, I do believe in karma and stuff like that, but not that nirvana stuff. Imo, it's impossible to stop all cravings (aka achive nirvana) if you crave nirvana.
Haruhism, imo, is the most "realistic" religion for me. The belief that one person is unaware of himself/herself being god, and what she wants is what she gets. I believe we are part of a dream. If we are un-dreamed, we just dissappear. And "god" will have then another dream to what he/she thinks is the perfect world. The only doubt I have against this religion is that the time that "god" has lived. This world has a recorded 2000 years, and even more. But who knows, maybe "god" wanted this world to have an intresting history.
So right now, I think that this world has satisfied our "god" so far. I know it has for me. Having fun and shit like that. I don't believe in dedicating your time to a dead guy you don't know.
That's what I tell my friends when they tell me shit like "Santa isn't real" and "why do you still believe in magic"
Edit: Plus, I don't believe in a Heaven or Hell, Some people do kind stuff because they want to go to heaven. Other people do kind stuff because of kindness. Don't you think "heaven" is kind of selfish if most people do good deeds because god told them so?