Of the options the OP mentions, I would go for the cable release, although a radio one would be even better. Not sure about the D7000 but I know that some Nikons (and other brands) have just the one IR receiver which is on the front of the body - not ideal for much apart from self portraits or groups including the operator. (It's possible to obtain or bodge a mirror arrangement to allow use from behind the camera but some can't be bothered) The range of the IR remotes also tends to be relatively short, while the radio ones work over many metres.