Honestly it'd depend on what I was doing at the time. My instict (assuming this is one of my good friends and not merely an acquaintance) would be too serve the time in prison; three years isn't all that long and it's certinaly worth my friends life. However, thats assuming things are sort of as they are now.
It's summer, I don't really have a whole lot on my plate, it just sort of feels like a big wait before real things start happening. Under those circumstances I can justify taking three years out of my life. But if I was, for example, married and had a kid, I'd have to think real hard about whether it was worth it. My instinct would still be to go but I might not because I have more important things happening. The same would be true if I was running my own company or generally being succesful and going places in life. That would make the choice much much harder becuase I'd have to abandon any progress I'd made to save my friend's life as opposed to just delaying making progress.
... It's a tough decision. I guess the real question is, how much would I lose? I'm going to lose something either way but, whereas the value of my friend's life is fixed, the circumstances of my life are constantly changing. If I had to choose between which to lose I'd choose the one that was less valuable.
Hmm... I always feel bad reducing ethical problems to value ratios. I feel like it dehumanizes the situation. Let me say that it would undoubtedly be my first inclination to save my friend.