I've picked Mark's gospel because it's all about Jesus (kind of obvious really) and because it's the shortest, fastest, most action-packed gospel out of the four. Mark doesn't even bother with the nativity, he's all about the action of the last three years of Jesus' life and focuses on that.
If Mark was writing a life bio of Jesus, it would be pretty rubbish as he's missed out most of Jesus' life aged 0-30! But Mark's not writing a biography! He's writing the 'gospel' or 'good news' about Jesus and that's why he narrows it down a bit. Does it mean that it's any less reliable as a historical account just because it doesn't tell us about Jesus' birth, childhood, teenage years, twenties, etc? Of course not. Historical reliability can't be settled that way.
Anyway I might be rambling slightly. Watch this space for some blogging on Mark. It'll be exciting and potentially life changing (encountering Jesus always tends to change us).
For now, if you're interested, here's a couple of short articles I've done about...
Evidence for the reliability of the gospels
Evidence for the resurrection of Jesus from the dead
Mark blog
