It depends on what your are looking for and the ages of your children. I have personally stayed in 4 of the 5 properties at VA Beach, the only one I have not stayed at is the Residence Inn. My summary is below.
Courtyard North @ 37 Street - This our favorite Marriott hotel in VA Beach because of the outstanding pool and have been staying there for the last 11 years. My daughter loves the pool because of the built in water slide and the water falls. It is one of the nice pools in VA Beach, but the water is always cold. The pool has a nice bar for adult drinks and also offers lunch type items. It is in the quieter northern section of VA Beach and the beach there tends to be less crowded than the other properties. It also has a nice indoor pool and the breakfast buffet is very good. There are a lot of good restaurants nearby, including Pocahontas Pancakes which is 3 blocks away. But all require a walk, or a ride on the VA Beach bus system which runs along Atlantic Avenue for a $1. At this hotel, we always get the larger queen/queen suite which works will for our family. The only downside to this hotel is there are only two elevators which are used by guests and staff and therefore can be slow and crowded. Note that this hotel started charging for parking last year and is currently $7 per night.
Courtyard South @ 25th Street. The hotel is very similar in layout and room configuration to the Courtyard North, but it does not have a outdoor pool. Same issue with the elevators as the CY North. There are more bars and restaurants in this area, so there is more vehicle and foot traffic. There are also more hotels and public parking lots in this area, so the beach tends to get more crowded especially on weekends. Note that this hotel started charging for parking last year and is currently $7 per night.
Fairfield Inn - The rooms in this hotel are smaller than either CY IMHO, unless you get a suite. Breakfast is standard FI offerings. Indoor pool only. Free parking. Crowded area, but lots of restaurants within steps of the hotel
Springhill Suites - Nice rooms. Indoor pool and nice outdoor poor. The outdoor pool has bar/restaurant with sit down service offering standard bar type food (burgers, wings, etc.). Several nice restaurants nearby including an excellent Italian restaurant (IL'Giardino) across the street (we will take the bus to the restaurant if we are staying at another property). Because it is closer to the south end of the strip is is not as crowded as the Fairfield Inn or the CY South. The only drawback at this hotel is that during the summer months there can be a long line in the morning for the free breakfast, especially after 8:00am. This hotel is our second choice in VA Beach.
Hope this helps.