The SD gecko is a faster and easier method when backing up wii games, however,because of the constant read function on the wii drive...it can wear out the lens of the drive faster compared to its normal intended usage. This is in extreme cases where the wii is constantly being use to backup games one after the other for a series of 8 or more game dumping per day. Using the LG drive method might be a bit longer but would definitely ensure that your wii is only use for in-game reading, thus, minimal wear and tear. I, however, use the SD Gecko method since I only create occassional backups and download the rest.
D2CKey does sound more advance (and complicated due to the high number of solder points and wiring involved) but is more costly compared to its wiikey counterpart.