I really don't like the popular Ella. All I can think of is elephant when I hear it. But I'm fine with Ellen. The extra syllable kills the elephant association.
Ellen used to be one of my favorite names when I was about twelve. It's no longer one of my favorites, but I still think it's nice. I don't think it's trendish at all. If anything, it seems a little post World War II-ish to me. It works well as either a first or a middle name.