I got AC on my 15 in MBP. I think it's worth it when a mainboard replacement can cost $900. I got AC on my first iPhone but I don't think I'll bother with AC on my iPhone 5. As for not getting a case... You do realize the iP5 is anodized and easily scratched don't you? I would definitely get a case. In fact I already have a case and my phone isn't due to arrive for some time because I don't want to carry it around for even one day if it means scratching it up. If I decide the iP6 or iP6s has something I just can't live without and I want to sell my iP5, I'll get a lot more for it if it's "virgin" because I've protected it in a case. BTW, they say the iP5 is the most rugged of recent iPhones but the black one scratches easily.
If I had to choose between AC and Squaretrade, I think I'd pick AC. I believe there is a version of AC that covers accidental damage and Apple customer service puts the rest of the world to shame. Even if it covers more and costs less, I doubt Squaretrade will treat you as well as Apple will treat you.