As I've said many times before, I am not a Jesus Mythicist, I am agnostic on whether Jesus existed or not. However, I'd like to take some time out to give Jesus mythicists some advice on what NOT to do:
1. Cite the work of Freke and Gandi. I have read "The Jesus Mysteries" and I have to say I was not impressed. When dealing with parallels between Jesus and pagan deities, oftentimes no ancient text is cited, and instead is the work of an 18th or 19th century mythologist. This is problematic because oftentimes these mythologists of old were imposing there own interpretations upon ancient myths, which means that the pagan parallels to Jesus are not as clear cut as you might think. I also agree with Skeptic Wiki's summary of "The Jesus Mysteries":
When researching the references that are supposed to back up Freke and Gandy's claims, several problems are found. In some cases, Freke and Gandy cite a claim in their main text and endnote it, but the source cited actually supports a different claim which is mentioned in the endnote but not the main text. In other cases, the source itself is misleading, sometimes because it is ambiguous, sometimes because it is unevenly reliable, and sometimes because the source is simply wrong. In still other cases, the source will even be misquoted. There are even claims which are bald assertions backed up by no sources at all, though this is disguised by surrounding them with claims for which sources are given. Often, these problems even appear in combination. The problems go beyond sourcing issues; Freke and Gandy also grossly misinterpret evidence.
2. Cite the work of Achyara S or Zeitgeist the Movie. Most of their claims are simply false. Tim Callahan has written an excellent article explaining why.
3. Cite pagan parallels to Jesus which you have not read about yourself from ancient sources. Although there are similarites between Jesus and other pagan gods, there is so much misinformation going around on the internet these days that simply need to find a translation of the ancient texts which describes these pagan gods and read about them for yourself.
4. Argue that pagan parallels to Jesus prove he did not exist. They don't. Certain themes in the lives of pagan gods may have been borrowed and pasted onto the Christian memory of Jesus, but this does not mean he didn't exist. A better argument would be that since Jesus has much in common with gods that other cults made up, it is simpler to suppose that there was no historical jesus (unless some historical evidence exists of him).
5. Argue that absence of evidence is evidence of absence. The fact that no contemporary of Jesus wrote about him is not at all surprising. Prophets and messiahs were as common in Jesus' time as Starbucks are in our time. Jesus' ministry only lasted a few years, and he lived in Nazareth, a fairly small village. It is perfectly reasonable to suppose that Jesus existed but that not too many people cared about his message.