What's there to even consider if you can choose to be immortal with a killswitch? Get every good thing of immortality without the whole "Forced to watch the universe eventually decay into nothing and then float forever in an empty void without release" -thing. Hell, even if you're planning on peacefully pasing away at the age of 80 to 90 or so, you can still just take the immortality. See what it's like, see if your plans have changed by that time. If so, live a few hundred years more a
So all in all, immortality with a killswitch all the way. Doesn't hinder actually ceasing to be when you're ready in any way, but has all the good sides of living as long as you want and achieving everything you could hope to achieve.
On a sidenote, would the immortality basically suspend my body into what it is now? Since that would be kind of a bummer because I'm hideously out of shape and finally working out again. I'd eternally be a fat tubby in that case, no matter how much I try to get my muscles to grow.