Firstly that's flat out insulting, If you enter a debate expect to have people challenge your beliefs, but do not be as low as to insult another un-involved religion. In the hope that a follower of it won't be their to defend it.
Secondly we have more proof for the exhistance of the origonal buddha than that of christ, we also know that christ when travelling in the east met a buddha and discussed philosiphy with him. Care to disprove your messiah?
Thirdly it's not about believing in buddha, it's just a man giving his thoughts on life, it's up to you to decide whether they are accurate or not. It's not really about belief.
And finally. I suffered from bi-polar and Uni polar deppression as a result of my conversion to christianity (nearly committing suicide at my conditions height), it was buddhism that got me through that time, and it continious to do so, to this very day.
Define happiness. Then we can talk about whether or not buddhism has helped me.