Orbit Power Sander

This is what I use on flat parts of a 3D print.  Make sure you start no lower than 220 grit, and don’t leave it on one spot for too long, since the heat can lead to distorting a PLA part.  Personally I start with 240 and then move up 320.

Keep in mind, the dust bag plastic part that connects to the sander broke the very first time I used it.  That part isn’t very strong.