I am going to get a bit technical, but you need to understand this if you are going to buy a wireless router.
Wireless routers use a technology called 802.11g (sometime just called "g" for the letter on the end). These are the current "basic" routers.
To improve the router some companies use something called MIMO to increase speed and coverage (so the router may say G+MIMO).
There is a new technology on the way called 802.11n (or "n" for the letter on the end). This will have even better speed and coverage.
BUT AT THE MOMENT 802.11N IS STILL BEING DEVELOPED.
However some routers are made which use the "n" technolgy and you may see them advertised as an "N" router.
These are the best routers to get, but note that if the "n" system changes at a later date they may not work. It is a risk you have to take if you want to buy an "n" router.