Vampire, a chance at immortality, do I take it and why... I do. I want to see how things turn out here and the advances, as well as the not so great things bound to happen. While there would surely be heartbreak, that's kind of guaranteed in a mortal life so why not get the bonuses of knowledge in an immortal one as well.
Siren, make any one do anything, what do I do.... In general, I'd like to make people be more aware of their actions. Even if people choose to continue to be assholes, at least be aware of how you being an asshole impacts those around you. People are a bit to careless with human emotions, I feel.
Genie, a wish that would be true and couldn't be reverse, what would it be... In relation to the first one, how about I choose some family, if they so desired, so be immortal as well. I'm not choosing a friend because I already know she doesn't want to be immortal, so she doesn't get to party forever with me.