Definitely blue-skittles.com/sour-blue-skittles/ as Jason says. The reason is that you want to make sure that both your domain *and* the page are relevant for the main keyword (blue skittles) as well as making sure that the page is relevant specifically for sour blue skittles. The search engines do not compose phrases from the keywords they find in different components of the URL. In your case you have these components:

domain - blue-skittles.com
file path - sour-blue-skittles

So if you do not include the words blue skittles in the path, the search engines are less likely to consider your page relevant for sour blue skittles and more likely to consider it relevant only for sour (that is as far as site structure optimization goes, of course there are other components to the relevance computation).

I wouldn't overdo it to a third level though, that is, the url blue-skittles.com/blue-skittles/sour-blue-skittles/ looks like an attempt to stuff your keywords. But here's a trick to make a bunch of pages relevant to keywords, by nesting. Remember that I said the search engine does not compose keyword phrases from different components of the url, but it *does* compose phrases from different keywords occurring within the same component. So:

blue-skittles.com/blue-skittles/sour/

would make your page relevant to sour blue skittles, and

blue-skittles.com/blue-skittles/sweet/

would make that page relevant to sweet blue skittles. Order within the component is not *as* important as occurrence, so relevance for sour blue skittles will be picked up even if the words do not occur in the same order.

The key here is to make your urls contribute as much as possible to the relevance of the page for the most specific search term you want to rank for, while at the same time not seeming like you're stuffing the keywords. The above is in fact borderline, because blue skittles occurs twice.

Hope this helps!

firstly this isnt what most people call link structure, it's URL structure.

link structure is actually much more important than URL structure.

like this is the future of Google rankings I believe.

this way - blueskittles.com/sour-blue-skittles/ still works fine but as with titles, just once with the kw is enough these days.

whether its in the main domain URL or directories / filenames, I think as Google continues to look for a more natural (less manipulated) web, why would you put the kw in more times than once if you weren't trying to manipulate rankings?

I would agree that's what you should do. we have a large powerful travel site that used to have directory structures like this

.com/luxury-hotels/uk-hotels/london-hotels/hotelname/

we re-wrote them all about 6 months ago to

luxury-hotels/uk/london/hotelname/

and across the board (500+ hotels) about 80% of them rose in the serps from 1-4 places, and as theyre mostly first page on the longtail deep pages anyway, this was a substantial improvement.

IMO it definitely wont hurt you going forwards to remove the duplicates