I rarely start wars, even when I should. It's just not my play style. The AI attacks me all the time anyway. <g>
I like fighting wars once they've started, but I like to be in a position of clear superiority. I'm afraid I'm a bit too cautious about defining what's "superiority."
My most satisfying victory was a recent diplomatic victory. I fought a couple of defensive wars, but mostly I developed, traded, conducted diplomacy. It was great fun.