Cards or dice?
This is a dilemma that I keep coming back to whenever I sit down to design or tweak a game. A lot of games want a random element. I'd actually go so far to say as almost every game wants one, for a number of reasons (it flattens out the difficulty curve a little, it means experienced players don't always win, and so on, but that's really another post waiting for later). So when I'm adding randomness to a game, or tweaking a random element, that same question keeps rearing its head. Does the game want to use cards here, or does it want to use dice?
Cards are really neat. I love them to pieces- there's enough space on a card for you to put some fairly complex rules stuff, and a deck of cards is essentially an X-sided dice and a lookup table, at least for the first draw. Cards work brilliantly if you want to have one of a great number of possible outcomes, and especially if you want inevitability. What do I mean by that? Well, if you shuffle the deck after every draw and reveal of a card, then the deck DOES work exactly like a dX, where X is the number of cards in it. Arkham Horror uses its location cards in exactly this way.
If you reveal a card and it goes to a discard pile, though, then if there's a great card in the deck? Every draw that's not that card makes it more likely to turn up next draw. The same's true if there's one really nasty card. That inevitability- waiting for the card that wins you the game or ruins everything- can make for some really great moments of play.
Cards can be held in hand, too- unlike dice, it's really easy to keep track of which cards you've drawn. Just hold onto them. That makes them perfect for resources- draw a gun from the gun deck, draw armour from the armour deck, draw blackmail material from the scandal deck. It's a really easy way to randomly hand out things to be used later, to get a delayed reaction from a lucky moment.
Finally, cards feel set in stone. This may be a personal thing, but I've come across it in a lot of people- there's no sense of personal responsibility for drawing a bad card. It was just a bad thing that was going to happen, and it happened to you. This can be used very cleverly within games- sometimes it's important that a big negative moment feels like nobody's fault, for example.
Dice are fun to roll. Every time you roll a die, you create a great moment of narrative tension- is it a good roll or a bad one, as it ricochets off someone's glass and spins in the middle of the table? There are always going to be a few seconds where you don't know. Dice work fantastically for quick moments of personal action in the game, but they require clarity. By that, I mean that I should ideally know before I roll the dice what numbers or symbols are good for me, and which ones are bad. That doesn't have to be the case on the very first roll of a die- for example, if there's a lookup table, or an unknown target number- but I should roughly know what's good. High numbers bad, for example. Or the game Ghost Stories, which has an example of the curse die; a die which has a bad result unless you roll a blank face. If a symbol shows up, even if it's my first time playing the game and I need to look up exactly what that symbol means, I know it's bad news. That's clarity.
One great thing dice do is that they make good results and bad results very personal. If you roll a great result, or a terible one, it feels like your victory; or your fault. in a very visceral way, they tie the player personally to the results.
So which to use?
While there are other randomisation methods, like tiles or a random number generator, they all essentially tie into cards or dice for me. so what does the game want? I've started using a basic rule- if it's an environment or a villainous action controlled by the game, I like to use cards. If it's a player controlled action, I like to use dice. It's a clean way to start getting the feel of a game right.
That's not to say that ends the discussion though- I can think of a bunch of examples of play in which I'd want it the other way round. But it's a good starting point for a discussion with the other designers or yourself. Consider whether you want inevitability, or a moment of tension. Decide whether you can boil things down enough for clarity of dice, or whether you want the space and memory of cards. What you shouldn't do is pick because of a limitation; if a design wants that moment of tension, say to quickly resolve a combat, then it wants dice. Don't go for cards just because your combat design is too wordy or complex- take a look at what your game needs, maybe redesign combat and put it into a later design. There are very few bad designs, but there are certainly places in games where a good design fits terribly.