Opinions on these cameras? I'm looking to buy?

I'm in high school so I don't have TOO much money right now, but Christmas and my birthday is coming up and I've got some in savings. I'm really into photography and I'm looking to buy a new camera because right now I just have an old point and shoot. I went into an Inkly's (camera/photo store) and a lady there helped me out a lot and showed me a few cameras that she thought would be good for what I'm into.
They were:
-Nikon 5100
-Nikon 3100
-Sony A33
-Sony A55
-Sony A45

I was wondering if any of you had these cameras or had opinions on them? I looked at them all and they all seemed pretty good. But, then again, I'm kind of new to this. I'd appreciate your opinions!

The best would be the Nikon D5100

although sony is a good company, in the DSLR world, you will want to stick to Nikon, Canon, and Pentax.

along with the Nikon D3100 and D5100, take a look at the Canon T3, T2i, and T3i

I'm not familiar with any of these cameras, however, Nikon has been making cameras for 50 years that I know of and have a reputation for quality. Sony although has earned a reputation for sound products, their track records in the digital camera area are not as good.
Buy the Nikon and even consider Canon.