No matter the grit used you will get swirls from an ROS. Hand sanding prior to applying the finish is the best way (only?)to cure this problem. Every woodworking project I do gets a final sanding by hand.

: 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.