imo picking how is high risk/high reward. we can flip my reasoning upside down and instead imagine that my heart would just stop beating in my sleep, which would be great tbh. i think that would be very easy to deal with, but as i said it'd be ever more horrifying to find out that you're going to die from a terrible cause of death.
if you choose when, i guess it'd be sad to find out you're going to die in 5 years, but when you've come to terms with it, you might begin to live. if i found that out, i'd drop everything in life and just live. drop out of uni, cash out my savings, travel, and do stuff i actually enjoy. perhaps i'll only get to live 5 years, but perhaps during those 5 years i'd also be able to live more than i currently will during an entire lifetime at this rate