It is hard for me to pin down exactly what the basis for my ethical perspective is. I think in a way I demonstrate a little bit of each in my decision making. For the most part, I concern myself with doing what will be best for everyone, or at least as many people as possible. In that way, I am most Utilitarian: the greatest good for the greatest number of people. BUT that is not the case in every single situation I am in. Sometimes I do "look out for number one" and do things that will be best for me, that would be more egoistic. Sometimes I follow the rules or the law no matter what, which is more duty-based. I also show concern about my relationships with people, which is care-based. So my point is, I don't think it is possible to pin down just one type of ethical thinking...at least for me. I can't speak for everyone. I believe there is a dominant one--and I said before that for me I believe that is Utilitarian--but there isn't only one.
While growing up, I think that my ways of ethical thinking did change and develop as time went on. When I was very young, I had a very egoistic way of thinking, as many children do. All I cared about was getting what I wanted, and being taken care of myself. But the older I got, and the easier it was for me to understand things, it changed. I became more duty-based. I followed the rules no matter what (or at least tried, haha) because mom and dad say so, and there is no other way. Once again, the older I got and the more understanding I gained, the more I learned to be concerned about others, and learned that it isn't always black and white, right and wrong. And through that knowledge, I developed the kind of reasoning that I use now.
I also believe that part of why I use a little bit of every kind of reasoning is that because I used each kind at different times as I was growing up, some of it stayed with me even as my mindset was changing. And I think it is that way for a lot of people.