Well I would have to say I have a good opinion for you here since that is my name! :)
I have always generally liked my name. It fits me. I've known about 5 other
Heidi's in my life. 2 went to high school with me. (I'm 26). The other two are in their 30's. One is about a 5th grader right now. I do think of a blonde person (I'm blonde and most
Heidi's I've known are blonde or blondish).
My middle name is
Kay and one other
Heidi I knew was also a
Heidi Kay. The other I believe was
Heidi Lynn. Don't know the other middle names.
I do like
Ella as well, although it is quite popular right now. I never used to like it, but it has grown on me.
In
America, I don't think of
Heidi as "nicknamey" as you will rarely see the name
Adelheid used or even
Adelaide.
Heidi is fairly common as a given name without being overused.