I quite like the RTD era and, by far anything from this revived 1.5 decades, it's the era which knew how to write 45 minute episodes concisely and in their entirety. Somehow, which the exception of the odd episode, the Moffat era forgot about that.
Dalek: it's a favourite for a reason. It nailed the Daleks, Eccleston finally came into his own and the show, for the first time in the RTD era, demonstrated that it could be nail biting. Pretty much the greatest Dalek episode of the revival era.
Midnight:less is more. Barely no locations, hardly any CGI, minimal score and no rubber faces (no, Tennant doesn't count). I should actually be utterly pissed off with this episode because it proves that once you remove the fat, padding and excess sugar, Doctor Who in the modern era can actually be engrossing sci-fi that answers nicely to the spirit of the original while absolutely giving it the modern treatment it requires to be relevant. It's no wonder the episode still works today.
Waters of Mars:the Doctor gets it wrong. And there's consequences for it to such an extent it makes me wonder whether he is a hero. This is the first time I ever felt this and, sadly, the last.
School Reunion: nope, it's doesn't all have to be dark and serious. This was a fun romp with a throwback to the classic era. I know some might think it was a little fanwanky (and, truthfully, the two women fighting over the Doctor was fairly crass), but I loved it. There must have been every temptation to turn this into a two-parter just to pad out the presence of Sarah Jane. But it didn't. It did its thing and left. Bless it.
Gridlock: just love it.