We have visited all of these beaches so I will throw my two cents in. I grew up in MD so we went to OC MD most of the time. Now we live in DE so we go to Rehoboth or Bethany Beach. We have also gone to the NJ shore which is very big around here. Last summer we went to VA Beach.
There are two main differences you will find at these beaches - the type of crowd and the level of activity. To me there is not much difference in the beaches themselves. What I have found with the NJ shore is people either love it or hate it. I personally hate it but know many people that love it. Generally there is a lot more activity there which I don't find very relaxing. But there is a lot to do. And to be honest, you have to deal with the NJ/NYC crowd which I personally find annoying after a while. We didn't like VA beach much at all. We stayed right on the boardwalk. While there was nothing wrong with it, it was hopping with activity and the town itself seemed rather run down. I do like the northern part of OC MD, but the lower part is very congested. We now usually stick with Rehoboth or Bethany. We always take day trips to Rehoboth because it is convenient and the small boardwalk is nice. If I was going to spend very long, I would go to Bethany. There is a lot less activity there but it is beautiful.
So it comes down to what you are looking for.
Atlantic City and maybe Wildwood may have some NYC people but OCNJ, Avalon, Sea Isle, does not. It is Philly, pa suburbs and south jersey who are the main representation. I think they are all very friendly.
Others are right about what you are looking for. There is a beach to serve everyone's needs.
VA beach - no rides, flat boardwalk, restaurants, tons of hotels, lots of traffic. The vacationers are the whole spectrum, nothing stands out more than another. Bush Gardens close by for another day option.
OCMD - lots of rides, attractions, lots of high rise hotels and condos, beach is tight and gets very crowded, boardwalk area full of motels, bars. High hispanic population on the beach by the boardwalk pier (I mean like NO ONE speaks English down there) Salisbury college students start heading into area by mid August. Avoid Biker Week at all costs. Northern end is quieter and much more family oriented. Average to very good restaurants up and down strip. Best one, Marlin Moon, is gone
Rehobeth - fairly quiet, small boardwalk, kiddie rides only, a few high rise resort/condos. There is a high gay population that lives/vacations there. Most people are okay with that but just wanted to mention it. Fabulous restaurants.
Bethany - So quaint and quiet. Not many places to stay just for a few nights. If complete relaxation is what you want, look no further.
OCNJ - family friendly boardwalk. No classy restaurants on it but there are rides, golf, water park, great boardwalk style food. All hotels (not many) are near boardwalk. The beach area is more condensed there, especially 4-10th street. The southern end is large 4-6 bedroom homes that are PRICEY weekly rentals ($5-7.5K a week!!) Entire city is dry. Philly and South Jersey crowd but all families. Restaurants are weak but Somer's Point have some good ones. Cape May Zoo is outstanding.
Wildwood, NJ
Huge beach - seriously huge. Best boardwalk rides for thrill seekers. Great water park. A lot of hotel options. If you avoid the weekend, it is doable, especially Wildwood Crest. Weekends are insane and where OCMD has bars, Wildwood has clubs and that increases the teens and 20's from Philly, NYC. Restaurants are average to good. Cape May Zoo close by.
Cape May, NJ
This is an option. Quiet, quaint but has some great restaurants and Wildwood boardwalk an easy trip for an evening. It is popular for weddings and has a lot of B&B's. Not a dry town but not full of drunks either. Happy medium