I would go for the engineering challenge.
I would fully understand the risk... the certainty that I would never again see my home. I'd never go scuba diving again. I'd never watch the sunrise in a forest. Shit, I'd even miss going to the gym! I'd never see my kids (they're 6 and 8) or any of their kids ever again. I'd never be able to pop down to the store and pick up a McGuffin or widget or a burger.
I'd never get another FP on Slashdot.
But I'd be on Mars. We'd be living with the leading edge of human technology, all alone, with no supplies ever coming by. Yes, I would die on Mars. Maybe within hours of landing. I've got somewhere between 60 and 70 years left on Earth, max. I'd get less than that on Mars, almost certainly. What I've learned, and learned the hard way, is that how long you live isn't as important as how WELL you've lived. Did you push your life to the limits? Did you live up to your potential? What do you regret not doing? Do it. Tomorrow never comes.
Think of what the species would learn from a mission to Mars. That's well worth my life and gladly traded.
And I'd do it for free. Just give me the use of the company vehicle for a few months, then room and board afterwards.