The euro ETF clearly has the most volume by a mile but I'm not sure I can agree with AI's conclusion that "FXE is clearly the best choice for a low cost, exchange-traded hedge against a weakening dollar."
FXE has been the volume leader of the bunch ever since the others were listed in last summer but, to use an analogy, Microsoft is not a better proxy for tech solely by the virtue of having more volume than Qlogic (QLGC).
Those two tech stocks are totally unrelated. The fundamental goings on with the seven different countries behind the currency ETFs may or may not be totally unrelated. Making a decision between several investments based on volume alone doesn't seem to make sense to me.
The chart below captures all of the single currency ETFs. Three other currencies have outperformed the Euro: the Mexican peso, the Aussie dollar and the British pound. The argument seems to be based on volume, which of course looks back but the volume leader has not been the price leader -- not even close. Looking forward the Euro may or may not be the top performer, but volume in the ETF will not determine which currency does lead.
Disclosure: FXA and FXS are client and personal holdings.