Some speedrun vids. In most cases, this is the fastest way through each campaign.
I'd suggest everyone learning to speedrun through expert campaigns as it really teaches you how to avoid and kill common infected FAST, making VS mode just *that* much easier... (case in point, 180melee)
https://www.youtube.com/watch?v=3VxnM2hvHvI
https://www.youtube.com/watch?v=d94Vy-XNFqM&feature=channel
https://www.youtube.com/watch?v=AyA46SCGQ6w&feature=channel
https://www.youtube.com/watch?v=Lm12I9A_d-E&feature=channel