They have this uncanny ability to out-do themselves every time The Doctor regenerates. Is this a good thing? Let's face it, Eccleston and Baker (next on the awesome-scale) were brilliant in their own way, but the only real contest is the proverbial 'out-awesome-the-other' contest between Tennant and Smith over the last few years.
You can't go past Tennant's ridiculously convincing, over-the-top acting that (almost) made me cry. Possibly more than once. He's just that good, alright? Anyway, he suits up every day, cruises around the universe befriending big heads in jars, saving entire worlds from certain death, all while rockin' a giant quiff. How they keep that thing upright is an impressive engineering feat in itself. It's really no wonder why every woman he comes across falls madly in love with him. They often die, but that's ok. It's usually justified because he gets all sad about it.
On the other hand we have number eleven. Smith's eccentric charm is only matched by this 'devilishly handsome' thing he's got going, even though it looks like a steamroller ran over his face and made it all square. Leaning more toward a more fickle personality and deeper psychological obscurity rather than a predictable emotional platter like his predecessor, we think he's definitely lived up to the challenge, and all that remains is to exceed Tennant's level of awesome, but in his own way.
I don't think words can explain that one properly, and until Smith leaves we can't be certain of anything, so this Chart I prepared earlier should explain things.
As you can see, Tennant & Smith currently retain such a high percentage of awesome, they have their own Pie Chart. For now, that's all we can determine.
We're all wetting ourselves with excitement over the new series that's been confirmed for this year, although we're not sure of the release dates.