I have the NHV adapter with his default antenna the 5 dbi one. So i want to change it and i want to suggest me some antennas. I dont know which is better the omni-directional or the directional so tell me to know Omni or non omni?
It depends on what you can get your hands on. I use a 14dbi (as seen in my avatar) for home and a 11dbi for mobile use. I got all my stuff on ebay.
Directional if you are trying to reach specific spots. Omni for wide area cover. Choose wisely. For home use 8-12 dbi omni is good but for longer ranges use directional panels/yagis/antennas from 18-24 dbi.
7dbi would be ideal if the AP is in your neighborhood. Otherwise you can go for larger setup like 14dbi if you are really worried about the signal strength. But it looks too heavy both in terms of setup as well as costwise. Choice is yours friend...
A 14dbi isn't heavy or costly, unless you find $16 costly. It's just at 7" square it is big for mobile use. I'd use an ALFA 7dbi panel or my 11dbi panel (4") for outdoors.