let me recommend what I use, which is an invisible shield + a carrying sleeve. That way, when it's in use, it's practically indistinguishable from an unadorned macbook but still protected from scratches, and when you have to carry it, it's got additional padded protection.
I'd rather not waste money on the speck case though. Get a sleeve + invisible skin for the same price. Also, invest in a keyboard/palm rest skin as well as a clear LCD screen protector (both on eBay for less than $15 each shipped).