On my woodworking forum, everyone says the Festool ROS is best, but it comes with a hefty pricetag. Here's my favorite sanding tip....
Use the vacuum attachment!!! Not only does it keep the dust out of your lungs and skin, it makes the sander work faster. Because it's sucking up the dust you just created, the sandpaper doesn't have to grind the dust over and over. As a result, the sanding goes faster and the paper lasts longer.
I learned this once when I had my boat at a yard that mandated dustless sanding. I was amazed how much more effective the sander worked with a vacuum connected.