Hard to pick a favorite. If I had to pick a personal favorite I'd say In The Mouth of Madness. I've never seen it brought up as often as The Thing or other Carpenter films, but it was the first "meta" horror movie I ever watched and I've always had a soft spot for it. Besides that, there are a few I make sure to watch every year. I have to watch Trick 'R Treat sometime in October and I usually start December off with Krampus (2015). Also, I'm not sure it even qualifies as horror, but One Cut of the Dead is a great one for horror fans or just movie fans in general, especially if you like lower-budget films and the passion that goes into making them. Admittedly the first twenty minutes or so can be hard to get through on the first viewing, but it's a great movie if you stick with it.

Least favorite I'd have to say, Lake Mungo. I don't think it's a bad film. I just went into expecting found footage horror and got a mockumentary about dealing with loss and uncovering a deceased family member's secrets. Again, not a bad film but not what I was in the mood for when I watched it.