General rule of thumb is, the closer you are to your root domain, the better. It is said, that Google weights subfolders in descending order. For example:
www.xxxxxx.com/card/wow/20-euros
2 .1 /3 /4 /5 5
That basically means, that your domain gets the highest rankingpower for its word(s), followed by the subdomain (if any), then position 3, 4, 5, etc.
And as Matt Cutts (from Google) stated (and recommends as a best practice): Google treats hyphens in URLs as a word separator, which basically says this:
www.xxxxxx.com/card-wow-20-euros
2 .1 /3 3 3 3
This allows all four words in your URL to score the same rankpower for each keyword: card 3, wow 3, 20 3, euros 3 instead of card 3, wow 4, 20 5, euros 5.
/cars/toyota/prius
-vs-/questions/is-it-better-to-use-slash-or-hyphens-for-seo