Much depends on the ages of your children. We stayed at the Beach Club our first trip because I thought the pool would be the best, but it was not! Our daughter had just turned 5, so she was independent but still needed to be watched like a hawk. Stormalong Bay is a terrible pool for that age! She was constantly getting in and out of the water, going to different sections and it was almost impossible to follow her around. This large pool winds around a lot with dead ends for people walking around it. There are bridges that go over different sections, but that got very tiring. I really hated that pool - it's much better for older kids. I also didn't care for the beach areas for the very young because of all the duck droppings there.
The other thing about the Beach Club is that it is a much less convenient location for getting to MK - you'll either have to take the bus or drive yourself. Although you can technically take the monorail, that is a LONG walk (probably 45 minutes with kids) all the way through the International Gateway and then Future World. Why tire yourself out before you even hit the park? Plus, you won't be able to get an early start since you'll have to wait for EPCOT to open before you can go all the way through it to the monorail. Getting to EPCOT from a MK resort is very easy, you just have to switch monorails once.
On our second trip we discovered the Polynesian and have never looked back. By then we had two kids, and being able to send Daddy home for a nap with the cranky baby while Mom and the princess stayed and had a good time was PRICELESS! Also, the MK fireworks are much better IMHO than EPCOT's. If you're at the Contemporary, you can easily pop over quick one night, or see them right from the resort. Plus, the boat parade before the fireworks is neat for the kids to see. The contemporary also has great restaurants. It's no contest - especially if your kids are young - go for a MK (monorail) resort with a pool that can be seen completely from one spot. Save the Beach Club for later.