What's a better lens for Photography?

I've been doing Photography for 10 months now and I shoot with a Nikon D3100. I'm 14 years old turning on 15 this December. I only shoot with my stock 18-55 and bought a 50mm 1.8. There both good lenses but I really think I need an upgrade. I shoot mostly landscape and allot of skylines. So Cityscape as well. I borrowed a 12-24mm from a friend and LOVED it. But seemed a bit off on the AF. But maybe it was just because its used? I don't know. And it was a Nikkor. But I'm also looking at the 10-20mm Tokina? I think thats it or a 14mm? I haven't really researched those lens so I don't know the differences between them besides what's wider. So what's the best lens for shooting City & landscape? What's the best brand to get? My dad said he'll get me one for christmas. So I'm stoked for that, but please. Give some informational facts about the differences and what brand to get etc. Please serious questions. Stupid ones will be deleted. Thanks

Here's some of my Flickr shots of Downtown San Diego & San Francisco

My God
I just looked at your photos on flicker. Amazing for 10 months shooting and 14 years old.
I bought the Tokina 11-16mm 2.8.it's wide and 2.8 is nice for low light. But after I bought it I wasn't extremely happy with the way extreme wide angles distort. Then I discovered
http://www.kolor.com/image-stitching-software-autopano-giga.html
You can use your 50mm and take multiple photos of a wide angle scene and stitch them together. You end up with a landscape shot without the wide angle distortion. Also you can bracket each individual shot and the program will adjust highlights and shadows like HDR photos. Wide angles make things seem distant, this doesn't. Don't get me wrong wide angles have their place. Before buying this lens I read about everyone on the market and this seemed to be the most popular.

I have the Tokina 11-16 F2.8 for Canon and I love it. It is a great lens. It is built like a tank and I have had no problems with it at all.

It is the only non Canon lens that I own with the exception of a Lensbaby and I would say it performs equally as well.

I chose the Tokina for the 2.8 aperture. The Canon 10-22 is a good lens but it has a variable aperture. As you zoom out the aperture gets smaller. I prefer my lenses to have a constant large aperture.