The incumbent, Mark Rutte, is considered to be from the free market conservative party. I don't think of the Netherlands as a free market country so I don't really know what that means. "Our ability to create jobs, our future growth, is built on the free market. It's built on open borders." - Mark Ruttehttps://en.wikipedia.org/wiki/People's_Party_for_Freedom_and_Democracy
The top challenger is Geert Wilders of the 'Freedom' party who has made a name with bold talk against Muslim immigration. They have been coalition partners as well as rivals. I can't comment on the Dutch immigration problem without bias; I was knifed by "immigrants" on my last Holland visit. I came out of it better than Theo Van Gogh did: http://www.nytimes.com/2004/11/03/world/europe/dutch-filmmaker-an-islam-critic-is-killed.html
Regarding Wilders, it's about time someone spoke up about the problem. Whether he is the best candidate, I don't know. Wilders has lost support in the last poll, but everyone seems to know after Brexit and Trump, polls on these matters have been amazingly unreliable.
This will be interesting to watch.https://www.ft.com/content/6bc14dee-0909-11e7-97d1-5e720a26771b