The one thing I can say is that the case makes the difference. I have a Targus leather case, a Brenthaven beauty with a sleeve, and a Lapdog. I never use the leather case anymore because it weighs more than the computer, and you have to open it up, take the computer out, find a place to put it, and then use the computer out of the bag. Same with the Brenthaven, except, with the sleeve, it's even worse. God forbid I'd drop my computer when I was getting it out of the case.
The lapdog (and other bags by
www.sjdesign.com) are incredible. They are light, durable, and most importantly, you don't have to take the computer out of the bag to use it. I take my lapdog, put it on my lap, unclick to clips, pop it open, flip back a protective flap, open my computer, and voila, I'm working. There are nonslip surfaces for your lap and the computer, and I've had it at about a 45 degree angle, and it never budged.
They now have a new feature with their laptrap. It apparently has built in "risers" to give you airflow under the computer.
I'm telling you, check out the lapdog, laptrap, and the other bags they have. I've tried a lot of bags, and those are by far the best.