also, think about avoiding holland as a whole when it comes to hitch hiking. It is the only place I have seen state mandated official hitching areas, but for a while now, its really hard as the students all get train passes now. The highways there are like a spiderweb, way too many for such a small country making for a hard time due to needing to watch every junction. But yeah, hitching should be the fastest, easiest way. Biking would be fun, and it shouldnt be hard to come up with a bike in Amsterdam. I second Blacknose about avoiding Paris, try to get around it somehow, maybe heading down the east of France through Dijon, Lyon, Montpelier... In the west its nearly impossible to avoid, all roads lead to Paris.
Also, It is quite easy to travel passenger train for free, if you are good with photoshop or gimp, and are interested, pm me for details. Interrail tickets are quite easily printed at home...