In your opinion, what is the best medium to use when attaching elements to your cake? I've tried different ones, but still haven't found one that I feel is really strong.
To attach to fondant or buttercream? What do you mean by "elements"? Just trying to get some specifics to keep from answering the wrong thing!
When working with fondant, I usually use water. Buttercream and royal icing are great glues also depending on what you're gluing and what you're gluing it to!
I use piping gel or gum glue.
If you're using fondant, then melted chocolate is like cement and will attach anything to it. You won't be able to reposition anything once it's on there and secured, though, it's going to be seriously stuck!