Go to where you're valued the most, even if where you are is pretty good. Sometimes leaving a good thing is hard -- but it can be good. I left my jobs pretty much when they became the most fun, but my career has been better off for it.
Getting a new job in a new org is always difficult. New people, new process, new everything, and you don't have your past reputation to gloss over mistakes -- which you're more likely to make in a new org than an old.
But ultimately, sticking around because things are comfortable might sound good, but you'll look back after 10 years and wonder just what you did.