Longer does not always equal better. The quality of the extended lifespan is key. But, if you could guarantee quality of life, there is still a bimodal distribution I find among my peers - "Why would you want to live forever?" and "Why wouldn't you want to live forever?"
FWIW, I'm in the "Why wouldn't you want to live forever?". Think of all the things to do and learn and experience and relearn. Ask me again in 10,000 years though.