generally speaking I have found that my ultrasonic cleaner demands more attention. Mine only runs for 8 minutes on a cycle, and about 3 cycles are required for good results. then the brass must be neutralized (I am using a vinegar/soap/water mix, the neutralization is necessary to prevent brass discolouration) and thoroughly rinsed and dried (in the oven when the wife isnt looking)
This method also cleans the inside of the casing and the primer pocket (if you deprime first)
The tumbler requires less babysitting, I set it up on a timer to run when I am at work (4 hour cycle seems to work well) and when I get home the brass is ready. The tumbler also processes more brass per batch compared to my little ultrasonic cleaner (although in my case the ultrasonic will process more in less time) I can also add a polishing compound to make it nice and shiny when it comes out.
The tumbler does not really clean the inside, and if you tumble deprimed brass the media will tend to get wedged inside the primer flash hole (depending on the media size) witch will require you to manually remove it.
Currently I prefer the tumbler, as it does not require me to babysit it and dry the brass afterwards, cosmetically the brass is nicer with the polishing action, and did I mention that I dont have to do anything with it until I feel like it? (if you leave your brass in the ultrasonic cleaner, depending on the solution you can end up with some interesting looking metal)
I hope this helps, I am pretty new to the whole thing so I am still experimenting to find what I like the best.
Good luck.