This is a HARD question, and there are no easy answers! Many times breeders have sold a kitten they thought was “pet quality” only to see it grow up into a stunning cat and wished they had kept it.
There are some indications that a kitten will be better than another, but kittens grow and change so much in the first weeks that it really is difficult to make that assessment when they are so young. It is easiest when there has been a previous litter from the same parents. Then you can possibly see pictures of how they turned out as older kittens or adults and compare that to baby pictures of the current litter to get an idea of how the kittens that are offered now might turn out.
Also, if you can see baby pictures of one or both parents and compare those to current pictures of them now, then you might get some clues as to how the their kittens will turn out as well.