The Job Pull

So about 4 months ago I was frantically trying to get a job - because the one I was offered was turned down. Now I'm trying to figure out how to set boundaries for myself in my current job, and how to turn down an offer from an incredible company, AND send out resumes to more companies because apparently I'm pretty popular at the moment.
Amazing how much time can change your situation.
I don't know how to tell the amazing company that I'm going to pass on their offer - I don't even know if that is the best decision! I have weighed the pros and cons, and I don't know what the 'right' answer is. But I think I know what the 'right now' answer is...but uncertainty is heavy! How you make decisions like that without your head exploding is beyond me - and suggestions are more than welcome!
So now, I am awaiting my offer from the 'big dog' because who doesn't want to work for a big dog in their field? I mean it would like working for a mom & pop computer shop, and Apple gives you a call and says they want you! Fabulous - I hope I have that feeling one day! So I'm waiting, and trying to figure out how to break it off with a company...that part kind of sucks.