I don't think he's the best actor on TV, but I think he's best actor as the Doctor out of the three new doctors, whether he's the best actor out of the three outside Doctor Who time will tell, he certainly shows promise. He was excellent in Christopher of his Kind.
I think they're all great actors, Eccleston and Smith were/are imo better at portraying the Doctor, whereas Tennant has excelled more away from the Doctor. Out of of all of them Smith has captured the weariness that comes with being an extremely old man trapped in a younger man's body the best, even when he's "clowning around" there's always something beneath it imo, you only need to watch the final episodes of Series 5 to know that. There's something special about Smith's portrayal, imo, and that's why even though I'll accept who 12 is (and not constantly hark back to Smith, or beg for his return

) Smith will probably always be my Doctor.