I pretty much only shoot "classic" longbows, mostly American Semi-Longbows, and "D" type English longbows. I have one slightly R/D longbow, and love it, but its still very much on the "Classic" end of the scale.
I love them because they are light in the hand, very quiet, feel natural to shoot, and with a good heavy arrow, penetrate like nobody's business.
I have several spanning a weight range from 35# up to 82#, but these days, I usually am shooting 60-70# bows. I hold them all the same way. Most are classic straight grips, a couple are slight locator grips. I really have no current preference, and the grip I use is pretty much the same on either. I've no experience with dished grips... need to try one.
I hold them like holding a suitcase. As you draw your bow, this seems to naturally pull the grip into the heel of your hand, if your elbow is very SLIGHTLY bent, and rotated outward, NOT locked.
I think a lot of the hand shock complaints stem from a few things. One: people trying to bring locked-elbow, modern, V-of-the-hand, lightly held, modern archery form over to a heavy longbow. Two: People trying to shoot arrows that are too light for a given longbow. Three: brace height not set up correctly.
The heavier the longbow is, the more these things are going to bite you in the ass, as poundage increases.
I've found that if you follow Hill/Schulz grip technique, Shoot a heavy enough arrow, and get your brace height right, hand shock becomes negligable. Provided you have a bow that is designed properly in the first place.
Regarding longbow design, I have one bow, a cheap 50# laminated "longbow" that is designed like a flatbow in the limbs (means limb lay-up is easy and cheap). No matter what I have done with it, handshock is foul. It is poorly designed, and that is hard to fight. One of the bowyers on here could tell you the why of it better than I, but I think it comes down to taper and mass in the wrong places.
Best advice: do good research and find a bowyer who knows their stuff, and specializes in the kind of longbow you want to shoot. Pay a little more for quality build, and design. You won't regret it, when it comes to shooting time.