I found some pictures of the current cast here 
(
there's 4 pics here too, but 3 are on the other site)
It is up to you all what you want, & I don't know anything about the show, but does the cast change regularly? Or do you at least know this doctor will be the doctor for a while? I'd be concerned over if your graphic would become outdated quickly if you focus on just one version of the doctor. However I also know that previous banners the board have had also focused on just one so its not like it'd be the first time if you did go with just the one version
An alternate thought could be to include favourite doctors as well as the new one (& possibly companions)? Or elements which represent other doctors? That could represent both the now as well as respecting where the show came from? Again, I don't know the show, so I don't know how feasible that is
Have you thought about colours?