Get both. they're both dirrerent animals. Forgeting about all the orbital action stuff, the round one will remove surface quickly and is excellent for fairing out strippers and flattining epoxy, glass etc. The 1/4 sheet pad or finish sander is best for between coats of paint or varnish. Neither will do the other's job as good as the intended item.
A drip of hardened epoxy wil take forever with the finish sander. Sanding between coats of varnish isno good with the ROS since it's too fast and aggressive and... you can't get super fine paper for it.

Don't get either withour a dust colector bag - spend the extra few bucks. I have the DeWalt ROS and a Makita Pad- both excellent.