Bigger props will make more commotion and add more flash which should lead to more attraction in dirty water. Depending on what your trying to acheive, I'd say bigger would be better until it causes line twist problems or becomes too much to cast.

The prop on wire in front of the hook would almost be a flyrod spinner. Putting it on the leader might work but I'd be worried about it knicking the line depending on how light the leader is. Thin metal edge rotating around mono or flouro for an extended period of time doesnt seem like the best approach.