Lens choice. Sigma 10-20 4-5.6 or Nikkor 18-55 for wideangle on D7000

Hello Experts,

I am looking for a lens to take landscape pictures. Though I can afford the sigma 10-20 (£340), if a Nikkor 18-55 (£70) is 90% there, or will be much more useful then will go that way.

My current lenses are the great 1.8 35mm, a Nikkor 50-200mm 4-5.6, and the 100mm macro which people here helped me choose.

I belonged to a walking group, and could always spot the new people, they would have every walking gadget that you can imagine, and sometimes stand out in lycra.

So far have only purchased a few useless items. Including a camera bag that would never wear around where I live, as it screams out 'Mug me, I have an expensive camera'.

Trying not to become the photographic version of the lycra fellow, and only get equipment that really helps, and keep the costs down a bit.

For general photography and landscapes. Would the 10-20 sigma be much better than the 18-55 at 18? Or will the 35mm be fine in 99% of cases?

Thank you.