This article is from the Getting A Cat FAQ, posted to rec.pets.cats newsgroup. Maintained by Cindy Tittle Moore with numerous contributions by others.
Consider adopting an adult cat. An adult cat already has a fully developed personality, so you know what you're getting. Adult cats generally adapt just fine to new homes, and "bond" just as strongly with new owners as kittens do. Also, adult cats are much less likely to be adopted -- most people want to adopt cute little kittens.
Kittens are terminally cute, but they can have many disadvantages. They require more care and watching over, they may not have the litter box down yet, and they go through a wild phase at around 6 months of age when they are unstoppable bundles of energy. Kittens need several trips to the veterinarian for vaccinations, checkups, and finally, neutering or spaying. Perhaps most important, it is difficult to predict what a kitten will turn out like when it grows up, in both looks and behavior.
If you do decide to get a kitten, try not to get one that is too young. Kittens should not be separated from their mother and littermates until they are at least 8 to 10 weeks old. Many breeders do not sell kittens until they are 14 to 16 weeks old, when the immune system is fully developed.