I have a fairly limited experience with speaker cables. For the first 3 projects that were single full range driver BLH speakers paired with 2A3 SET amplifier, I used solid core copper cables. They seemed the perfect match to my ears. Focused, natural and full bodied sound.
When I shifted to a 2 way design using a 12 inch bass driver, I felt it sounded better with stranded wire. I used 12 AWG Supra classic cables for external wiring and 14 AWG for internal wiring. Supra cables use tin plated copper. Somewhere I had the feeling that it adds a slight colour to the sound, though for all these years I was liking it.
Now that I am starting a new speaker project, I decided to use stranded but pure copper cables. Mogami cables are known to be absolutely neutral sounding, partly due to their legacy of making cables for Studio applications. I have always used Mogami 2803 RCA interconnects and the speaker cables harmonizes the entire chain.