8. The Master
As famous as the Master is, I feel we should not have to see him for a very long time. Before we carry on though, just know that I thought John Simm played the Master brilliantly with the right amount of crazy Time Lord aspects. I feel the Master has come to the end of his story for the moment, and so does not really have a reason to return. If he is to return, it should be a surprise that makes everyone excited to see what his episode will hold, rather than having the reaction of "Really? Again?" It is now clear that the Time War will feature at least a little in the 50th. So if the Master was to return, it would have to be through flashbacks, and I believe this could happen. Luckily, as John Simm's Master was from the RTD era, it would be hard for Moffat to write him in the same way as Davies did. And so if the Master is to return, I just hope it's not John Simm portraying him.