I was never able to get much of any actual results from ultrasonic, and i probably tried a dozen different solutions and formulas at another dozen different temps and another dozen different time intervals.
SSTL is the way to go, without a doubt. Read this thread on TFL - the .40 brass you see pictures of is my brass that another poster used as guinea pigs. It was enough to convince me on the spot when I got the brass back to source up a Thumbler's tumbler and go stainless, and I will likely never go back.
I have two Lyman vibratory tumblers that have not been turned on in over a year now. I really ought to sell one of them now that I think of it. The Firing Line Stainless Thread
One thing I do do that seems to make a bigger difference in the finished product is use the wash-n-was car wash solution you get at Autozone or Wal-Mart. It leaves a very thin wax film on the brass that does a couple of things - it protects it from tarnishing and it leaves the brass slightly lubricated (much like you would have with a walnut vibratory tumbler and the old standard cap full of NuFinish car polish).
Regular soap and citric acid does a great job, but it strips everything from the brass. Which isn't a bad thing, other than allowing the brass to tarnish faster and meaning you need to spray lube it even with carbide dies, simply to make the loading operation easier (hell, I still do this anwyay).
And buy citric acid in bulk off of Amazon. I paid $17 for 5 lbs of it delivered the other day. That will last probably a year, even with me using it in the dishwasher as a water softener and rinse aid.