I've used Berroco Comfort, Wool Ease and Vanna's Choice. I've always wanted them to be washable. I love berroco comfort because it is so soft. Joann's has a new yarn out by someone that I can't remember the name of.
There isn't a "best" yarn for anything. The "best" choice is that which suits your purpose. Do you want wool? Do you want machine wash/machine dry? Do you want a yarn with good stitch definition that suits the pattern your making? Do you want to spend a little or is that not an issue?
All that said, I have used superwash wool (in particular Cascade 220 superwash) and had excellent results with machine washing. I'm a big fan of Encore (as Gelliott mentioned) because it's very easy to care for and comes in a wide range of colours.