If those are the two options, then I think the skimmer is a must. If you want to use your canister, use it for circulation and a place for carbon and Live Rock Rubble so that pods can have a place to reproduce safely, otherwise they can start to become a nitrate/ammonia factory. That's how I use my canisters, but I think a skimmer is a must.
There really is no comparison between a skimmer and a canister filter as far as what's more important. Skimmer wins, hands down, but you can use a canitser filter effectively in a salt water tank too, in addition to LR and a skimmer.