Stigma 10-20mm EX HSM DC 4.0-5.6 VS Nikon 35mm 1.8 AF-s?

More as of which one is sharper and Better in low light, I'm a Landscape photographer

Dunno about Stigma, but for landscapes, the Sigma is a better bet. The Nikon is fast, but it's a little long for good landscapes - it may be the sharper lens, but it won't do the job as well as the zoom.

Best in low light would be the Nikon lens. I agree with the other person about the wider Sigma lens being better for landscape photography though.

The 35 isn't wide enough for landscapes. Just use your 18-55 @ f5.6 or 8 and learn about hyperfocal distance. If you don't have a tripod, get one.

Stigma lenses have a bad reputation.

Apples and oranges, and it would seem that you "want" to be a landscape photographer. If you actually "were" a landscape photographer, you'd already know this.

The Sigma is a super wide angle lens, at the 10mm end almost a rectilinear fisheye. If not used properly, it will introduce massive distortion into the photo.

The 35mm lens actually is wide enough to shoot landscapes, since you can shoot landscapes with a 300mm lens if you want. No law says you have to use a lens wider than Xmm to shoot landscapes. The 35mm is much faster, 2.3 stops to 3.3 stops faster than the Sigma, but that isn't what is important for landscapes. A prime lens is generally sharper than a zoom, and that does matter.

The 35mm is also a better "general purpose" lens, although a little wide for my taste. Some people like wide primes, others don't.

Before you get too caught up comparing these two, perhaps look at the Sigma 20mm f/1.8 or something like that for your landscape work.