I can mainly speak to the black walnut varieties - the improved selections, like Emma Kay, Thomas Myers, Clermont, Pounds #2, etc., have thinner shells(think easier cracking!), and a much higher kernel percentage - I've seen one lot of Pounds #2 nuts that cracked out at 55% nutmeats, whereas the typical wild-type BW tends to run more in the 15% range; most of the better selections run in the 30-40% range - and the improved varieties yield much more in the way of intact halves/quarters, as opposed to kernel fragments.

Heartnuts - quite a bit of variability in cracking characteristics, mainly with regard to 'pinching' &/or release of the nutmeats. Also, in my area, late-vegetating selections are preferred, in order to avoid loss of crop due to late spring frosts/freezes.

Carpathian walnuts - somebody else will have to weigh in; I've never been impressed with any I've had occasion to sample(undesirable astringency), and the Easter Big Freeze Disaster of 2007 killed all I had grafted back to their BW rootstocks.

Hey Amiart
I know some very good varieties of Walnuts for home production.
Ashley
Chandler
Chico
Daniels
Howard
Hartley and
Padro

Nurseries like Nolin River Nut Tree Nursery can provide some ideas. As a good example, Nolin River has chosen about two dozen preferred Black Walnut cultivars (and has descriptions for about a dozen online right now), over a dozen Persian Walnut cultivars (descriptions of ten available on their site), five Heartnuts, a dozen Butternuts, etc.

Here is a link that might be useful: Nolin River Nut Tree Nursery

Here's a list of some other nurseries you might check. (I haven't checked them lately, so I'm not sure what you'll find, but I think all of them offer nut trees and have a decent reputation.)

Bay Laurel Nursery - multiple types of fruit and nut trees and plants - very good G.WD. rating - www.baylaurelnursery.com

Boyer Nurseries & Orchards, Inc. - multiple types of fruit trees and plants and nut trees - limited, excellent G.WD. rating - www.boyernurseries.com

Nolin River Nut Tree Nursery - persimmon, pawpaw, & multiple types of nut trees - excellent G.WD. rating - www.nolinnursery.com

OIKOS Tree Crops - multiple types of fruit and nut trees and plants - excellent G.WD. rating - oikostreecrops.com

St. Lawrence Nurseries - various northern climate fruit and nut trees - excellent G.WD. rating - www.sln.potsdam.ny.us

Van Well Nursery - various fruit and nut trees - excellent G.WD. rating - www.vanwell.net

Whitman Farms - small-fruit plants and trees and nut trees - excellent G.WD. rating - whitmanfarms.com