To the brains trust

I have a Nikon d200 and generally use my tokina 12-24 for landscape photos. I have been thinking about getting some nd filters

One option is a screw in 77mm ND Fader Filters which look flexible without having to purchase multiple filters.

Another option is a cokin filter holder which would also allow me to get a grad ND.

What should I get? If I went for the cokin will the P series cokin Work or do I need to get the z series? Or will both still have problems at 12mm?

Any advice appreciated

Thanks