The "boxed" version is much better given that you are maximizing the internal volume edge to edge. If you let the edges taper, you can't put as many things inside, which means you have to make more compromises. That's why I think Apple has been leaving the tapered designs versus boxed designs to help differentiate the lower-end, entry items such as the iPod Touch and MBA from the iPhone and MBP. Granted it's not consistent across every product line since the iMac is somewhat tapered versus the boxy Mini and the iPad is slightly tapered as well (probably necessary given the size and manner of use), but this is a theme that might end up extending to those designs in the future too.