My Christmas rankings:
1. Last Christmas
A collage of riffs on Alien, The Thing, Inception, and a little bit of Miracle on 34th Street, all of which come together really well, serving as a nice coda to Dark Water/Death in Heaven and, more largely, the Doctor and Clara's frayed, complicated, and weirdly loving relationship from S8.
2. Twice Upon a Time
I wrote some longer thoughts on it
here, but I thought it was a really lovely episode and a powerful, touching swansong for both Capaldi and Moffat. The regeneration scene in particular was a wonderful summary of what Doctor Who means to them, as a message for the next generation.
3. The Christmas Invasion
Even in spite of relatively little time on screen, this is a great debut for David Tennant as the Doctor, and remains one of his and RTD's best episodes. Second only to The Eleventh Hour for modern Doctor intros.
4. The Husbands of River Song
What a shame that Twelve and River only have this one episode together; Capaldi has far more chemistry with Kingston than Smith really ever did, and their dynamic elevates this episode several orders above the silly but fun story around them.
5. The Time of the Doctor
A fitting end to Smith's run: messy and unnecessarily convoluted at times, but with some wonderful, heartfelt character moments, in particular the final 10 minutes, when Clara returns to Trenzalore and the "Four Knocks" music kicks in.
6. A Christmas Carol
I've never had any great affinity for the Dickens story, which is why this is so much lower than most people would place it. But it's still a well-made episode all the same.
7. The Snowmen
I think this one is underrated! It's good fun, in large part because of Jenna.
8. The Return of Doctor Mysterio
On paper, a really dumb, awful-sounding idea. In execution, way more charming and fun than it had any right to be.
9. Voyage of the Damned
The first not-good one, imo, but still solid nonetheless. A dopey, turn-your-brain-off sort of blockbuster.
10. The Next Doctor
I don't remember much of this, other than David Morrissey and a giant Cyberman. As such, I have no real feelings about it, positively or negatively.
11. The Doctor, the Widow and the Wardrobe
Basically the same as the above, except I remember even less about this one.
12. The End of Time Part 1
So bad, it left me genuinely worried for a week that RTD was going to fuck up Tennant's exit. Luckily it recovered a lot in part 2. The "Books of Saxon" bit near the beginning has to be one of the worst all-time Doctor Who scenes.
13. The Runaway Bride
The only one I couldn't even bother to finish, which by default makes this the worst. Ironic, since Donna went on to be such a great companion in S4.