I don't mean to sound crass but what strangers on a travel website think will make a better birthday present for your girlfriend is irrelevant. I'd venture to say half the people will tell you to pick the trip and the other half will tell you to choose the show.

You know your girlfriend better than any of us so it's really comes down to your decision. You could, ask her what she'd like but that would spoil the "surprise".

So, just pick one option and let it go at that. The upside to your dilemma is that regardless of which option you pick you can always do the other one at a later date - say one for her birthday and one for next Christmas.