Of the ones you mentioned, UV/Clear filters really are generally rather useless, unless you actually make a habit of leaving greasy fingerprints on your front lens element. A hood gives good physical protection without any chance of compromising image quality, unlike a clear filter. I'd skip the UV filter, unless actually shooting on the beach on a windy day or something like that, where it would give protection the hood cannot.
Polarizers must be used with care on ultrawide lenses, as noted by another poster. The darkening effect on the sky only happens in a very restricted set of angles vice the sun; an ultrawide catches so much sky that this will appear as a narrow dark blue band which looks extremely odd. Polarizers are still useful for cutting reflections off glass or water, and have surprisingly good effect on surfaces such as roof-tiles or stone. I'd get a polarizer, but be careful about how you use it!
Graduated ND... the screw-in ones are a so-so idea generally speaking, they require you to place the horizon dead center which is rarely where you want it to go. The square ones from Cokin or Lee or what have you that you mount in a frame in front of the lens can be very useful, but are a bit time-consuming to adjust just right... OK for tripod use but not for handheld. Solid ND filters on the other hand are good to have, either for dragging the shutter speed or for opening up the aperture in bright light.
Re ultrawides: Some are absolutely not designed to be used with filters, ie the ones with protruding bulbous front elements like Canon's 14mm f/2.8L or the Nikon 14-24 f/2.8. The ones without such a front element do not pose this problem, but you should be aware that some filters can bee too thick, physically, so that the filter frame shows up in the corner of the image of an ultrawide lens. Not a good thing - on such lenses stick with the dedicated "thin" filters that are made for this purpose.