Themails7:
the one which have the more possibilities (supported protocols b/g/n..., supported encryption)
That would be most of them since all of that has to be handled on the shield itself and not by the ATmega.
Themails7:
the fastest one (throughput speed, limited of course by the Arduino communication speed itself)
That would be all of them.
Since cost isn't a concern, get the Official Arduino Shield.