I only use a combination of wired and wired over house mains in different locations, but if you really want to stick with wifi then Hawking Technology is the place to go for a wide range of directional antennas, I still have a 100m one that used to travel on vacations...

Similar discussion with some good advices:

Fyi: best buy has a $32 WiFi extender : gadgets

Just what i need , a hawken wifi. cheers

I was talking to the owner of Super Power Supply

Super Power Supply Official Store

About an improved antenna situation for my house with thick concrete walls. Below is his response, which may help you.

Quoting 

The best antennas depend on the situation. If it is a point to point link then a directional is best as it reduces the amount of interference from other networks, if the router is going to be in an area with client devices all around it then an omni is going to perform better. Also with any antennas you aren't getting something for nothing. They work by reshaping the signal area. Your signal area is like a balloon with your routers transmit power being the air in the balloon, then the higher dbi you go, the more you push down on the balloon, so you loose signal vertical but gain it horizontal. That is also why it is best to put the output power at the highest level your router supports without distortion. Most routers do this by default, if using DD-WRT or third party firmware it takes a bit of experimenting. 2dbi provides a more spherical shape like a baseball for example, while 9dbi provides a flatter signal shape more like a frisbee. To answer your question in short, I would recommend the 9dbi foremost, then adjust the orientation of the antennas in such a way to provide best directionality of the signal. The best orientation for you depends on where your client devices are located in relation to the router. I would try | | |, _ | _ , \ | /, etc, and see which provides the best throughput. The signal is provided in a donut shape around the pole of the antenna, for reference. For reference, each model of omni is a different size as well if size constraints are an issue, 2dBi - 4.5 inches in length 6dBi - 7.5 inches in length 7dBi - 11 inches in length 9dBi - 15 inches in length

Mike