I would say that, on a regular basis, peace is the best feeling to have. The less distractions there are, the better you'll be able to focus and channel the emotions of the characters. For example, if I really get into my writing, I'll start to feel my character's emotions take over me. If they're mad, I'll start getting angry for no reason. If they're sad, I'll become somber, etc. There is only one instance I can think of where the opposite was true. I was really frustrated with the whole query process of publication and I was having a bad day all around. I had about twenty minutes left to write and I was so mad that I hadn't produced anything good, that I somehow channeled that pure rage into one of the most concise query letters I've ever written. While that rage ended up being useful, I can't recreate it, nor would I really want to. That much anger isn't good for my blood pressure.