The best tool to use for sanding curves is a drum sander. The thing interesting to note is that drum sanders come in all kinds of sizes and even different textures aside from all the different grits and types of sandpaper.
For very small work, there are miniature drum sanders that are used with the hand held rotary tools. Even here there are three sizes of drums. You want to choose the curve of the drum that most closely matches the curve you are trying to sand. Working with a very small diameter drum on a much larger curve tends to create grooves.
You can also get larger drums for use with regular hand drills. Then tend to work better with corded drills rather than battery operated drills because of the higher rotational speeds.
Very large drums are available for use with drill presses where the drum will be stationary and you move the material. You can even get a fixed sanding machine that has a table with a drum sander that comes up through the table, moving up and down slowly as it spins rapidly, using the sandpaper more evenly. A specialized sanding machine like that is of course the easiest to use.
Most drums are relatively rigid. Some require sandpaper in the form of a drum, but some use regular flat sandpaper that you attach to the drum, saving a lot of money on paper. Some drums are actually like tires in that they are blown up with air and present a very flexible surface for sanding. These require special flexible sandpaper.