Replacing Antennas

Please recommend me replacement antennas for the following 2 routers:
1) Buffalo Airstation Giga Nifty WZR-G144 DD-WRT (images to help recognize connectors) http://forums.techguy.org/members/74...-antennas.html
2) ASUS RT-AC66U (U.FL, RP-SMA)

I need +9dBi omnidirectional - pls consider Asus' already + 3dBi/5dBi gain.
All routers/clients lie on the same (+/- 3ft) plane.

I am afraid to buy the wrong antennas which could curtail some functions/capabilities/specifications so, please, recommend me a specific brand & model, possibly with good cost/performance.

Thanks in advance for the help.