I usually use the cardas solder because I had a large roll for the longest time that I haven't gone through but I have noticed a significant difference using mundorf silver gold solder.
I swapped out the driver wires in my Final Audio Sonorous III headphones with 24 gauge mundorf silver gold wire and mundorf silver gold solder with amazing results. The sonic improvements are easily noticeable even to untrained ears. If high quality audio is what you're looking for, its gonna get expensive. High quality things are expensive sometimes, it is what it is. Big difference from cheap wiring and solder designed just to do the bare minimum functionality.
Don't listen to the people who say it doesn't work or they don't hear a difference, meanwhile they've never tried it.
the result was probably more because of the Mundorf wires. (silver/gold wires with factory insulation has a "flat and even" signature)