I just bought a Thule 1600 Evolution. All of the new Thule and Yakima boxes have quick attachment hardware, so they go on and off very quickly (the first time I put it on, it took about 5 minutes - less to take it off)
I would recommend the new silver top boxes of either line. They cost a little more, but are lighter and won't get as hot inside from the sun as the black boxes do. Better for your stuff.
I noticed that a lot of stores are moving to the more bag-like setup. With advances in materials, I suspect these will work as well as boxes as far as protection from the elements, but I would be afraid of it scratching the top of your car since I don't think they can sit up on the rails like the boxes do - of course, I could be wrong.