Your question about brands is a bit meaningless -- they all have a range of models, some better than others but most rely on a small number of chipset manufacturers and the products from different brands frequently perform in a similar way.
The real choice is between big names brands such as those you mention and the unknown cheaper models. Because they too use the same small range of chipsets -- they perform just as well in many cases -- but the the difference may be noticed later when you look for advice or driver updates -- the big brands mostly have good online support and they'll probably be around in future when the small brands have disappeared.
The differences between G and N are to do with wireless reception, range and speed.
The speed of your broadband is probably lower than the speed of the basic 802.11g wireless (even taking into account that the true performance of wireless is seldom even half the claimed speed).
If you opt for 802.11n at present you would be well advised to buy the router and the wireless adapter from the same brand to ensure compatibility.