The thing I found which made the most difference was getting rid of the idiotic ends these vendors put on their cables. Once I figured out that there were extra ends for the cable sleeves and used them...not only did they fit better...but looked 1 million times better.
Are you talking about ferrules for cable housing? They can improve the look and fit of your cable housings, but they don't make much difference one way of the other to braking power or shift precision.
I use brass index-shift cable ferrules on both brakes and shifters. They are sturdier and truer to size than brake-only ferrules, and they hold up better in the long run.
But the more important thing is to grind or file the ends of your cable housings square and flat. This keeps them from tilting when the brakes are applied (which adds mush to the system) or chewing up the ferrules with their cut ends. It's this sort of subtle detail that distinguishes quality bike mechanics from pretenders.
Chalo