Which Apple iMac should I buy?

I'm looking at buying an Apple iMac desktop computer. I love the features, the design and of course the reassurance of buying an Apple product. My problem is, there are so many!! I'm looking for an iMac that would suite a family, including young children. It won't be used for business. I would like a reasonable amount of storage space, but not overly massive. I your opinions, what are the pro and cons of buying one of these machines? Thanks.