What I have would be the Omni 32". I also (not listening to the salesman ) have a yaggi directional. And like you you have to know where your tower is to use one. I'd say dig around in here, and if you have questions I have called them before as to what to use and such.
http://3gstore.com/index.php?main_page=index&cPath=53
Honestly the Omni was enough, rarely is the yaggi better. Yeah I switch back and forth once in a while just in case. I am 2.5-3 miles from my tower.