I know (Antennas is a full 1 year class for Telecomm Eng back in Havana) that is why the practical aproach of asking around or closeby posters on forums is not a bad one IMO. Too many variables and choices and also important there is no better antenna , it all depends on the particular application, all variables have to be taken into consideration.

91XG is a high gain antenna and as you can tell from the pictures it has lots of director elements therefore it is highly directional (25 degrees beamwidth) also note the reflector is a mesh V shaped reflector therefore it has a high front-back ratio so it will kill signals coming from the opposite direction , you will need a rotor to use this and therfeore is suitable for a 1 TV solution and DX'ers.

Once you see the superior picture quality of this HD OTA signals compared with cable or satellite pay services you will more likely end up cancelling it and probably requiere a multi-TV solution.

I get all those 24x7 (except CHCH, ION, NBC they depend on weather/day but you can not rely on it, I use a 2m Dish for those except CHCH I dont care) with a 20 dollar monoprice.com antenna, small,white, with amp in it and easy to install, suitable to distribute to several TV. I could not beleive its performance despite its small profile and rather simple looks. So easy to install too and has a bendable small plastic pole that allows you to install it to any surface. It is outdoor on the wall , 9 ft , and feeding 3 tvs in Mississauga.