I tend to agree with the last poster...with an adult, you know precisely what you're getting in personality and health. Besides, there are millions (yes, millions!!!) of homeless adults who have been living in shelters waiting for forever homes...kittens certainly have it easy. Everyone loves cute baby kittens!!! They get snatched up immediately, with really little effort. Adults, unfortunately, tend to get passed over...and when many adopting families decide that they're bored with the kitten, or the kitten didn't grow up to be what they were looking for in a grown cat, they then go to live in a shelter. Very sad, and it happens everyday across the world.
Unfortunately (and I do love kittens as much as the next person), I believe there is very little you can do to predict how a young kitten will mature, and what type of personality it has. There are individuals who train, cuddle, nurture, and manage all of those crazy kitten behaviors in hopes that they will be "shaping" their kitten into the perfect adult companion...however, I belong to the group of people who feel that kittens grow to the cats they are destined to be...kind of like people, too. That doesn't mean that the kitten won't thrive and grow in a loving home...because we know that they certainly don't thrive in an unloving environment. But like humans, kittens are born with their own personality traits.
Here's two examples of what I'm talking about. I brought home 8-week old Ripley (torti female), thinking she'd be a playful partner for 1 year old Fergus...she was playful in the pet shop, frisky, active. I thought she would play like that forever! Well, at 3 years old, she can still be fairly playful, but she's turned into a very needy lapcat. I would have never known that from her kitten behavior. And now, to present times, I have added my third cat to the mix, 10 week-old Steuben. I brought him home from a farm at 6 weeks...he was a lover!!!! He nuzzled me, cuddled in my arms, purred, ugh! Well, two days later, he has become a complete spastic ball of energy, and a force to be reckoned with!!! He is INSANE!!!!!!!!!!!!! I love him to death, but I actually have no idea what type of adult cat he will be.
Pick the cat or kitten that speaks to you...and then go from there, because as kittens, it is hard to predict personalities.