If we are just talking speaker wire, it's pretty much a toss up, buy the cheapest, but I do have some comments to make. I do have some Monoprice speaker wire that has discolored over the years. It's odd, but all of the exterior of the copper even under the insulation has gotten the green color to it. Oddly, I have some other Monoprice cable that is different AWG, bought at the same time, and it has NOT done this. I'm thinking maybe the insulation had some contamination on that spool. Regardless, it doesn't affect the sound, but I don't like to see it.
RCA Cables:
I really like the BJC, but note that some of their cables are very stiff and can't be bent well. I don't remember the model #s, but I prefer their more flexible cables.
I also really like mediabridge. The few cables and adapters that I have from them are top notch!
Monoprice--while these are fairly good quality, for me they tend to have connections that are too tight. They work on some of my gear, but not all of it, so I tend to avoid that.
Banana Plugs:
These are by far the best that I have found:
https://www.amazon.com/gp/product/B006U3O566/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
These are pretty good too, make a nice rugged connection with 2 set screws. I often discard the outer jacket on these and use heat-shrink instead for a nice slim connector.
https://www.amazon.com/gp/product/B005E1CGZC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1