If you don't have a breed in mind , why not adopt 2 kittens from a shelter? http://www.petfinder.com/index.html
If you do have a breed or even a certain breeder in mind, you need to be researching that breed (and breeder) in particular.
Good place to look for breeders & start researching breeds http://www.breedlist.com/
13 Questions to Ask A Breeder http://www.breedlist.com/faq/breeder_questions.htm...
Determining a Breeder's Reputability http://www.bengalcat.com/aboutbengals/reputable.ph...
Or if you think you'd like a pedigreed kitten but you want to find out about more breeds, you could visit a cat show.
TICA Show Calendar http://ticamembers.org/calendar/
CFA Show Calendar or list http://www.cfa.org/modules/EventCalender/EventCale...
One cannot make any truly meaningful broad generalizations about the chance of problems in breed cats vs non-breed /"domestic SH/ LH" cats. Basically within the purebreds there is the best chance AND the worst chance depending on where you get them.. And in the domestics it's a total crapshoot! .
I agree with Mocha, the absolute worst chance of getting a healthy kitten/cat is a purebred (or supposed purebred) from a bad breeder - like the kitten mill kittens sold in pet shops, or kittens from irresponsible, ignorant BYBs maybe breeding on a smaller scale than a mill but just as irresponsibly.
OTOH, probably the best chance for a healthy, well socialized kitten/cat is from a really responsible breeder who is very concerned with health and doing any available testing appropriate for cats in general and their breed in particular, carefully choosing breedings, feeding high quality food, keeping kittens for 12+ weeks with lots of human handling and love, etc. Pedigreed cats from good breeders are also selectively bred for temperament, so they've had things like being attached to humans bred into them for generations. Put that "nature" together with the "nurture" of the socialization they get and it really is pretty wonderful.
(But this is NOT to say a domestic can't bond strongly with you. they absolutely can and do.
The "domestics" are....who knows? some can be very healthy, some very unhealthy.
Actually many random bred cats are themselves doing more inbreeding than most breeders today would do. it's just that nobody is recording their pedigrees. One dominant tom can sire most or even all the kittens in a feral colony or small neighbourhood area of indoor/outdoor pet cats, then he goes on to breed with his daughters and granddaughters, or is deposed by a son or grandson who breeds with his sisters and mother and aunts...... it can wind up with a very inbred group. (So much for the "hybrid vigor" someone mentioned. Actually that is not even an appropriate term for random bred domestic cats. For the most part they are NOT hybrids of different breeds, but a population of nonbreed cats.
But in general the domestics are not as unhealthy as poorly bred purebreds from bad breeders.
Whichever you get, choose alert, responsive kittens with bright, clear eyes, no runny nose. Pick kittens who come up to check you out (unless you WANT to take on the project of a really shy / semi-social kitten from a shelter.) Talk to the breeder or shelter workers who know the kittens about what you're looking for and which 2 female kittens would make a good pair. Littermates is a good idea.but at some shelters they have kittens from different litters kept together in one room and you might find 2 girls who have bonded while at the shelter. or maybe at a foster home.
Re FEMALE and MALE . It's not that females can't be affectionate. but I think it's that they are more moody about it..Female cats can be super affectionate --- when they're in the mood. the males are more steady in their affections.
(and I don't just mean the females who are not spayed, though that certainly accentuates it. The queens are often totally caught up in their hormonal cycle and in rearing kittens, and do seem to be less friendly. In fact less friendly than intact toms. But hopefully you'll be getting kittens already altered, or else with an agreement to have them spayed by a certain age and you will keep the agreement.)
Another interesting thing.... many people feel that the female cats are in general smarter.