North Myrtle, IMO is the best area for families with smaller children...though the differences aren't as great as they used to be, North is still the more spacious, quiet area.
South Myrtle is pretty crowded and the teen Spring Breakers, Senior Weekers, etc. tend to populate there. The Pavilion and other major attractions are located in South which makes traffic heavier there too...
Of course you will probably want to venture down South for the attractions, and larger restaurants, but as for a place to STAY and which beach is the best, I'd say stay further in the North section.
There's a Ripley's Aquarium there that ROCKS! There are huge tunnel aquariums with sharks and giant sea turtles. The place is packed with all sorts of neat stuff...last summer my parents let us come along with them on vacation there and DS LOVED the aquarium.
MB has some really cool miniture golf courses - our fav is the Captain Hook one...I think the name of it may just be Hook...but it is definitely a nice pirate themed course complete with a giant ship and all the bells and whistles.
If you like shows, the Alabama Theatre and Broadway at the Beach always have some cool ones.
Shopping at Barefoot Landing is AWESOME! So many neat shops to look in.
The Pavilion is an amusement park with a large selection of rides - ones for tiny ones all the way to the big kid stuff. I think there are go-carts there too.
Let me know if you have any more questions, I'd be happy to help you out!
