Doug, it depends I guess on what you're trying to accomplish with the sanding. If you're trying to feather out some rough edges after scraping then a machine sander is your best bet. If you just need to sand to smooth a bit and create a bond, then some elbow grease and a selection 50 or 60 and 80 grit papers is the better way. You could use both, though the square area on exterior trim that could benefit from a machine sander is usually not that great, usually just the barge board, lol. I'll sometimes use a machine and do everything I can with it in the area I'm working, then put that down and finish the rest by hand. Machines are more effective and efficient on field work, like expanses of siding. Again, as to the type of machine, a belt sander cuts pretty deep rather fast so I would only employ that if absolutely necessary. A belt sander is also very cumbersome for anything other than working on a flat surface right in front of you. I find very little use regularly for mine, but I go through two palm sanders a year.