The D3300 should be skipped entirely for the D5300, as it offers far better autofocus, performance, advanced shooting features (e.g., bracketting), and better access to manual controls. Cost about $150 more.
At that range, the powershot G1x should not even be considered, its image quality is far worst along with the performance for its price range (easily outperformed by morrorless cameras at half the price.
the 70D is just not worth it unless you need its video features (which I would recommend waiting for magic lantern to come out for it first). Still image quality is still worst compared to many cheaper DSLR's, and at low ISO's there are many mirrorless cameras that perform very closely to it. (with the exception of the autofocus especially in low light)
Unless you can get the D3300 for less than $500, skip it entirely.