Well, either a USB adapter with attachable antenna or a WokFi would work good.
With a USB adapter with a attachable antenna, you can attach an antenna of any kind to it (making sure its the right fit first). So you have the choice of using an omni or a directional antenna.
The WokFi will also work. Its a cheap solution, but an effective one. While what im about to talk about doesn't have much to do with the design of the one your looking at, or the mobility of the one your looking at, it may give an example of the abilities of a home remedy for WiFi connectivity.
I built a dish out of a paint can cut into four section, and in between those section, I taped tin foil. I then taped a USB wireless adapter (AWLL6080) to the center of the dish. So in the end, I had a big, bulky, immobile WiFi dish which couldn't be taken anywhere without being mounted on a tripod, and even if it were to be taken around everywhere, it'd be a real pain to keep up with. So I tested it in many places (backyard, on roof, etc...).
Our first test was having the adapter operate by itself, without the dish. It picked up a sad 3 to 4 AP's. Then on the roof it picked up about 5, but nothing more.
Then we taped the USB device to the center of the dish. On the ground, I discovered about an average of 11 to 12 AP's, while also keeping in mind that this test was done in a neighborhood with many trees, foliage, and homes. Then we took it to the roof where we tested it. We found then, a total of 15 AP's. The jump in sensitivity was surprising. At first, i thought this would only turn out to be a piece of crap i spend hours working on for nothing. But, its proven that home remedies can often bring the best results. (The attached image is the dish WITHOUT the tin foil between and holding together the divided flaps).
But anyway, for the purpose your planning to use it for, either one would work for you. Personally, Id choose the USB with detachable antenna so that I could attach a hi-gain antenna to it, and not have to worry about dragging around some kinda of external piece of hardware, like a dish with me where ever I go.
(lol, kinda dragged this post out didn't I?

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Borgslayer