I've had a lot of experience soldering on brass in the past year so
I empathize with your delima.
It depends on the composition of the brass you are working with of
course, but I have been using 14K easy and hard solder with good
results in both the color and the quality of the solder joint.
One thing I learned really fast was that if you didn't get a good
solder seam the first time, you will want to stop and clean the
pieces to be soldered getting all of the pink off of the metal. When
brass has been heated too long and/or too hot, copper in the alloy
will rise to the surface of the metal giving it a pink cast. It is
going to be very difficult to get a good solder seam until the pink
is removed. You may get the seam to solder without removing the pink
cast, but you are likely to have porosity beneigh the surface that
will weaken the seam. I have used silver solder but depending on
what you are soldering, it can be visible and if you get it too hot,
it can pit the surface of you metal.
When I find myself in your same frustrating situation I sometimes
have to be reminded to step back and go over the soldering basics.
Chances are you will find your answer in one of them...Cleanliness,
Fit, Flux, Solder, and Heat.
In my limited experience, when I can't get a piece to solder it most
often comes down to heat. Either I am using the wrong size flame and
therefore not sufficiently or correctly heating the pieces of metal
and the joint to be soldered, or, I have overlook an obvious heat
sink that is drawing heat away from the joint to be soldered.
If you are still have trouble getting the seam to solder properly,
please describe for us the set up you are using to solder the pieces
and the size/mass of the object(s) you are soldering.