Hey, how exciting for you getting a kitten soon! I'm not the most experienced of people having only chosen one pair of kittens ever but I'll tell you what I did before others come and give you better advice
It's easy to see if a kitten comes from a good genetic background if you get a chance to see its parents and have a look at its pedigree. Obviously seeing the cats in person is the best choice but if you need to make a quick decision phone the breeder(s) and write down the pedigree names of the cats a few generations from the kittens you're considering. You'll get something like "Llandar Coolhand Luke". If a google search doesn't show you pictures of that cat, the first name (llandar in this case) is the name of the cattery and you can have a look at their website and look on the studs/queens pages. This was enough for me as I only wanted pets and was satisfied that they had very good looking parents. I also liked how the kittens looked. If you want to show them at some point there are specific things you should look for (
http://www.bengalcatforums.com/forums/v ... c&start=15 pages two and three are really helpful) to see what are good 'show' traits.
Healthiness is something you can see in person. Don't get any kittens that look sniffly/too skinny/runny nose etc. Make sure they'll be vaccinated before they go home with you. Many breeders do HCM testing which means parents are screened for a genetic heart disease, you may want to check they've done this as well. I'm not sure what the risk is if you buy from unchecked parents or how common the disease is. You'll also be able to see how friendly the kittens are, the more sociable they are the sooner they'll settle in with you (although most kittens can be drawn out of their shells with patience).
If you stay uncertain or like you don't know enough to make you happy I'd say let these go and keep looking, it's not a decision you want to rush!