Personally I'd say that the CycloWiz has the edge over WiiKey, as it can only be upgraded with the use of an switch that puts the chip into development mode; in other words, it's unlikely that any future releases will be able to nefariously disable the chip, which is why I ended up getting one.
That said, whatever you decide to go for, make sure that your system can take a modchip (i.e. you've not got the D2C chipset, or you're capable of 'repairing' the cut legs on a D2B if you've got one).