I'm struggling with the choice between Eventing and Dressage as well, but for now I've chosen Eventing. Don't worry too much about the choice now, just go with what you want and need. If that changes then you can change with it :)
My goal is to go Novice before deciding which sport would be better for me. I'm in the same place as you, I love both sports but can't choose exactly what to focus on.
I also dream of competing in the Olympics one day. Maybe it won't happen but I'm going to do anything I can to get there ;)