So I will be touring Europe a bit this summer. I know for sure that I will be buying a Eurail 15 day Global Youth pass (yes, I am still that young), and my general itinerary. One route seems to concern me, however. Me and a friend will be going from Madrid to Geneva, and the trains ex-BCN to GVA seem to be scarce. On top of that, train reservations will cost more than airfare (after combining the flight with my other intra-Europe flight, all while improving my previous flight's times.)

Considering the summer traffic, on this route specifically if able, would it be better to book the flight or take the chance of standing by for 2nd class for one of the trains? I've heard that SE France is very beautiful to pass by on train, but I don't want to get stuck in Spain when I want to be in Switzerland.

All help appreciated.