For my hand sanding I use the following:
1) 5" DeWalt and 6" PC ROS (my primary sanders, used probably 70-80% of work)
2) DeWalt 1/4 sheet OS (for sanding edges and gentle sanding of thin veneers)
3) Fein Multimaster (for getting into corners and areas that neither of the above can reach)
4) Sanding Sponges (to quickly touch up corners the other sander's missed or odd profiles)
5) Sanding Blocks (typically for quick touch up or hand sanding)
6) and very rarely -- profile sanders (either PC or Fein Multimaster)
I also have the Ridgid Oscillating Spindle Sander which comes in very handy for other odd jobs. And for really detailed sanding of thin edges and curves, sanding bands for my scroll saw can come in very handy. Additionally, I also have some pneumatic sanders as well, but they simply duplicate the above.
I would not part with any of my sanders. Though I may use my ROS for the majority of my work, they are not ideal for all tasks. YMMV