Sometimes a kitten chooses you, then it's easy except if you wanted a female and a male decides you should choose him instead.
A buyer or a pet Aby is typically interested in three important factors:
Usually in the order listed but they would be well advised to reverse the order.
Looks and personality are judgements. Health is a bit more objective but nonetheless in some respects difficult to ascertain. If there is no observable health problems among any of the cats and kittens, likely their are no current health issues.
Then it is simply selecting the kitten that most appeals to you. If you're lucky there will be only one kitten available. This may sound counter-intuitive but choosing one kitten our of several can be very difficult. As soon as you think you made a selection another kitten does something endearing. Often and with the client's permission we have had to selectively remove kittens from the room in order get down to the single kitten the client most wants. The selection process when there are several kittens to chose from can take hours.
Also keep in mind that kittens do only three things: eat, sleep and play. If you're looking for an affectionate kitten and the kittens are in scamper mode, they may not be very huggable. Similarly, if they are played our and your kids want to have them chase a toy they may not be too active but they will be huggable. These phase changes every few hours and if you don't rush your visit you'll see all of them.
Occasional buyers will visit well before the kittens are ready to go to their nw homes. Their personalities are still developing. Occasionally a kitten that wasn't appealing say at 10 weeks of age, is most appealing at 12 weeks. Be patient, give the kittens time to grow.