What are you sanding - wood or a varnished surface?

The ROS Random Orbital Sanders do create a random orbit so it covers it own paths. Oscilating sanders or most pad sanders make an orbit. If you are using an aggressive paper, yes, you will see some circular scratches. Normally they are used for fine sanding 220+ and not to cut away a lot of material. I've used pad sanders with 120 grit on decks but I always do a final hand sanding with the grain or strips before laying glass. I don't go too fine or more than 150 grit for pre-glassing. Between varnish coats I use my pad sander with 220 on the first coat wet and then up to 400 grit wet before my 2nd or final coat. If I go a third coat I go even finer and just get rid of the gloss surface.

For cutting and fairing wood or epoxy, I always use my ROS.