As a happy Sony Alpha owner I agree with Sarah
The main caveat in favor of the Nikon is progression. If, sometime down the road, you think you will be promoting your efforts to a more advanced body, then Sony leaves you to make the leap all the way to an expensive full frame model (which means replacing your lenses). Whereas Nikon has DX format intermediate steps such as the D90 and D300.
But the A450 is such a nice value you could almost regard it as a bridge you can afford to burn.
Canon EOS 50D, Fujifilm F45fd, various film dinosaurs