I didn't like the mini-cup brewer because it seemed to me the water ran through too fast to get the full taste of the coffee.
I find many coffee brands bitter, but lately have enjoyed Dunkin Donuts Medium Roast. Then, they must have messed up a whole batch because it's been bitter the last few bags.
I'm going to try the salt thing.
You may want to try a light roast, it wouldn't be toasted as long and may have a less "burnt" taste, but be aware a lighter roast has more caffeine. I've had to mix light with medium or dark roast to prevent the jitters. I usually only drink a cup a day.
I like to buy from the bulk section and read the descriptions -- I look for one that says it is full bodied but has a smooth taste.