Clarke for John Connor? I could get on board with that, he is one of those actors who is yet to have a starring role (though that will change with the Apes sequel next year) but has always given quietly good performances.
He certainly looks big and tough enough to be the leader of the human resistance, and he is a good actor as well.
As for Taylor, I dont think we can judge him on TDW that much. All of that movies problems were down to Marvel, they wanted him to add all the humour in, they wanted the run-time that short, they wanted Malekith's back story cut down as well as some other things in the movie.
I liked TDW but if Taylor had been left to his own devices I think we would have got a better movie which would have been more dark and serious in the right places. I am willing to give a chance with Terminator 5 for this reason, despite being a HUGE Terminator fan.