Edit: Forgot about the comment from one of the randoms in today's round. I had used it on approaches in the fairway on Par 5's as well and had a short Par4 which I used this to tee off. He was walking as well while his other two buddies rode. He made a comment while we were going down the fairway about how I sure liked to hit that club and asked what it was. I kinda smiled a little.
Putter. Last year in our member guest I had a must make birdie putt on the last hole of our last match. It was about an 18 ft putt with a right to left break. The opponent was sitting about 8 ft away with a par putt getting a pop and we were tied with them. I drained the put center cup and he then missed so that we won the match and our flight. That was an awesome feeling!
If we are talking full swing clubs then I would say the PW would be what I want in my hand for a full shot that I have to hit.
I had to think about this one for a bit. I don't know that I have a favorite "go to" club, at least in general. The only thing that comes to mind is a wedge. If I can look at a green with a wedge in hand, I'm feeling good.