wiikey V1 is no longer maintained and requires soldering on your part.
Wiikey V2 (and almost ALL newer mods) have the ability to have a no-solder option. That said, if you had a newer wii (either no exposed drive chip or an epoxyed chip) you will have a heck of a time to get it installed if you have no experience prior to such things.
In which case, I suggest you get the drivekey. The benefits are that it works on absolutely every wii no exception and requires absolutely no soldering since you're just placing it on the drive cable.
The downside though is that drivekey is limited to playing backups at 3x speed (same as soft mod). So if you never had a problem playing with softmod speeds, you won't have any problems with it either... but if the slow read speeds bothered you, you'd be better off with a more traditional chip.
Of the different brands of modchips, I've heard the best with Wasabi and and Wiikey V2 but I honestly have no first hand experience with either.
