This was kinda hard. D:
#3: Umbreon
I love every single Eeveelution, but Umbreon used to be one of my favorites. Though it's not anymore, I still love it, and it still makes it as a top 3 favorite dark type. It's adorable, but more than that it's just so awesome. I always imagine it running through cities and forests in the dark, just being so cool. Its shiny form is also very pretty, and its bulk is incredible. Though I haven't used one in a long time, I can still safely say it's up there as my favorite dark type, and will always have a special place in my heart <3
#2: Houndoom
Houndoom is one of those pokemon I always admired from afar; thought was totally awesome, but never really used one. However, it still makes it to my favorite dark types list, due to its dual-fire typing (I love fire type) and truly awesome design. To be honest I really love its mega form too. Not much else to say about it, it's just simply stunning. <3
#1: Greninja
Oh man, I love this thing. Especially with Protean. It is so much fun to battle with, especially since it's super fast and has a lot of coverage. In addition it's just so... cute! Have you used it in Pokemon Amie? oh my goodness. It's like an adorable little yoga instructor. And your best pal. All in one. <3 <3 Gotta say, even though Fennekin is ADORABLE and definitely holds the award for "Kalos starter I fell in love with first", Greninja impressed me a hell of a lot more than Delphox, and though I do like Fennekin more than Froakie, I love Greninja more than all of them put together. Never thought Froakie's final evolution would end up being my favorite dark type.
Honorable mentions: Liepard, Mightyena, Skuntank, Sableye, Absol, Honchkrow