Do I have any hope of living more than a week and getting off the island someday?
If no, C. May as well go with something easy so I can have the most fun with it.
If yes, G. Then by the time I'm rescued 5 years later, maybe, just freaking maybe, I'll have the hang of bending the lower holes on low harps without it sounding like a sputtering mess. OK, make it 10 years.
3 choices: C and G (for both reasons above), and throw in low F.
5: C, G, A, low F, E. I'd be tempted toward a Bb or D as my last choice, but the E would give me the most total range.
That's all assuming they can be any kind of harp I want. If I had to select from my current collection, I'd go with C, A, low F, D, E, which would give me my favorite harp models and the most variety of them.
If I had to choose one, I'd be super-vanilla and go with C.
Three of them, I'd probably have to choose C, G, and A.
Five of them... It'd be C, G, A, D, and... Huh, man, it's like asking which children to sacrifice... I'm gonna have to go with Bb, though. Guess my high-pitched children can die. XD