If I could choose, I would live a solid 150-200 years and then die. I selected this lifespan because, while I do not want to die too early, living forever would be a pain. I would make sure that I am always supremely healthy and up-to-date on the vaccines in order to achieve this lifespan. The benefits of this would be me watching the world as it goes by, and joining my friends in Heaven after not too long of a wait. The problems would be diseases and sadnesses such as watching the world destroy itself because of humans.
I can go more in-depth if you want, but I'll do that tomorrow.