Probably the Charger, and Hunter.
For one, I love the adrenaline rush when you start sprinting and barge straight into a group of survivors, sending then in all directions and knocking them down, then standing there merely crushing the first survivor you hit into the pavement.
And the Hunter just because they are so versatile and edgy. I love watching it when I pounce some survivor from 50 feet and proceed by ripping chunks out of their chest.
If I was ever in a zombie situation, the least two zombies I would want to find in a dark building are a Charger and Hunter.