I've bought two high-end carbon frames over the last 3 years. One with external and one with internal routings.

The frame with internal routing is outstanding, in terms of weight (<900g), stiffness, ride quality, aero profile ... everything.

But the setup for the internal routing was wretched misery - something that I do not plan on repeating. A few months after getting this bike running, I bust a front derailleur cable, and the fix requires I pull out both cables (front and rear derailleurs) and re-install. I could not be bothered, so a $5,000 bike hangs on a hook. I have a fleet of other bikes.

There are a lot of great bikes out there, but I'll purchase ones with external routing.