I wouldn't know, since my horse doesn't express his preferences as far as tack goes, and works well in anything. I have used a sweet iron curb on him, but stopped because I wasn't happy with the mouthpiece. Again I wouldn't be able to tell with him.
I don't need one, or use the one I have, but I'm just curious if the taste really made that big of a difference for your horse? I know some horses can be picky about different metals, and prefer the sweet iron taste.
Does the taste stay the same from the start, or once it starts rusting, does the taste change?