But that doesn't mean you can't say which one is your favourite! Let me know down in the comments what your favourite moment from season 4 was, and which season is your favourite! So if you haven't seen Sherlock yet, beware of SPOILERS in the comments. But I think you should be alright, considering no one comments or probably reads this anyway...
What I will say is that the ending for season 4 is really heart warming and nice :D