It's advisable to have a separate banner on the same page but in a different location. This way you can eliminate the variable of the domain name. Testing involves many variables and it all depends are the goal of your promotion as to which you would test. Clearly, its a numbers game and the banner that garners the most hits.
really depends all on what the web site is and what you belive will get sales or people for you. No body can do that for you just think about it you being on the other foot and what your looking at if it will get you to join or buy.
