What Polariser do i need?

[Rooky007]

Ok I have a cokin Kit and i want to get a polariser for it rather getting a screw in one.

But what do I need as i want something to help the sky blue and the like.

Also what is the best price people seen the screw in one for just incase they can be got cheap as a extra

 

[Rooky007]

Ok have any of you tried a screw on polar with the cokin holder on the same time. I would have thou when we move the polar to right place the cokin would have to be squared up after and this would move the polar wont it?

What is actully wrong with the one you can get for cokin?