Tumbler if you just want it shiny. Ultrasonic if you want to clean inside and primer pocket. My ultrasonic came from Harbor Freight (and looks exactly like the ones the reloading distributors sell), and cost the same as a tumbler. It's not really messy. Just pour the solution in and dump it when you're through.
(And it's a lot faster! 480 seconds or less compared to 4 hours or more.)