C300 and mkiv Jetta

Not a fan of the use of blur. Especially how you included the mirrors (and the clouds in the reflection). A little more time would have gone a long way, and perhaps if you're going to simulate depth of field where the cars are at should also be in focus .

I like the second except for that puddle with tire marks.

On the last try selecting the wheels and using radial blur rather than just bluring them. It will add more of a sense of motion

the second one's probably the best, though the car's facing the wrong way.

Most of the other pics have a few things wrong with them...fake blur, light standard growing out of the roof, ass end of Prius growing out of the side, just straight awkward positioning (the nose to nose shot), etc...

#1 & 5: Why so much room between the cars?

I don't care for the car almost running into the frame of the image. Give it some room to 'move into'.

Lotsa' links! First shoot with moving cars need advice.

Nice shots. What settings wereused for rolling?

In my opinion, the green is overdone. Perhaps reprocess #2 with less green and make the dodging over the car only apply to the car, and not the area around it? If it weren't obvious you could dodge it out a fair bit and it'd look really nice.