Your typical wifi box has vertical polarization. The notebook wifi cards are horizontally polarized. This doesn't seem very well planned.
So wouldn't it make sense to have circular polarization, especially if you are building antennas for stumbling purposes?
For a somewhat different question, some high power cards have two antenna connectors. [SMC2532W-B] Does anyone know if this card polls both antenna connections? What I am leading to is you could do your stumbling with two different antennas, one H and one V, letting the antenna choose on the fly.