Another thing to consider:
Cases protect your investment. A good case is a heck of a lot cheaper than a good AEG.
And if you go with a solid color hard case and throw the right stickers on it, passersby are more likely to assume that it is a keyboard than a gun, which can make life a little less tense.
Also, my experience has been that showing up with a Pelican case draws almost as many oohs and aahs as the SAW inside the case does. And a big chunk of airsoft is about th 'cool factor'.
Buy a good case. Spend a little more, and you get better quality. Bring a tape measure and measurements of what you want to put in the case with you when you shop for the case, leave at least a half inch of wiggle room on your measurements, and always, always, always physically measure the INSIDE of the case rather than the outside.
If you get one with multiple layers of foam, you can trace what you are putting into the case with a sharpie and just trim the foam to fit. It takes very little time, and the results look a lot more professional.