Just taking a break from practicing and got to thinking about this. My first answer to this question was going to be the key of E-flat major. The piece I was just playing ends in a low E-flat major chord, and I just love the way that sounds. Goes right into my soul. Then I did a brief flip through books sitting on my piano and discovered that many of my favorite pieces are in D-flat major. So now I am changing my mind. I like D-flat best. But then almost as many pieces I like are in A-flat major, which to me is an easy key to remember – you know, just spell the word, b-e-a-d /flats. I guess the question is not as easy to answer as I thought it would be. I will stick to E-flat and D-flat major because of the way they sound in lower register harmonies. Anybody else have a favorite key?