Another vote for Lassie here, too. Oh, how I wanted a Collie growing up, with that beautiful long, flowing, coat of fur. I think most kids in that era did.
If I had to choose another animal hero that I wanted and would never be able to have, it would be Flipper. I loved dolphins with all my heart and still do. My dream for my upcoming 50th birthday is to swim with dolphins. It is actually possible to do this in San Diego at Sea World, but it costs quite a bit to do. Unfortunately, right now is a very stressful financial time with my husband starting his own business. So that dream is out of the question. Maybe for my 51st birthday. (sigh)