Johann Nepomuk Hofzinser once said that playing cards are the poetry of magic.  I love that expression.  The only problem with it is that not everyone who likes magic likes card magic.  I never really understood this, but I recall Jeff McBride saying in a lecture that some people feel intimidated by a magician with playing cards, particularly people who gamble.  "When you walk up to someone locked and loaded with a deck of cards it can [put people off.]"

On the other hand, cards can be one of the most versatile, flexible, and accessible props in all of magic.  Cards allow the magician literally hundreds of different effects with one prop.  Balancing this wonderful advantage against some the people who aren't huge fans of card magic is something I weigh on a case by case basis.  Generally, I like to start with something a bit more left field and away from playing cards, then transition to cards in an organic way, and then back to the more abstract magic I like to close with.  Still, cards are the prop I always have on me, and in a pinch, my favorite magic to perform.