Set oven to 400°F (205°C). Prepare a baking sheet by lining it with parchment paper or setting a wire rack on it.
Wearing disposable gloves, slice every jalapeño lengthwise into halves. With a small spoon, remove the seeds and white membranes.
In a bowl, stir together the shredded chicken, softened cream cheese, buffalo sauce, shredded cheddar, blue cheese (if using), and ranch or blue cheese dressing until evenly incorporated.
Spoon the chicken mixture into each jalapeño half, creating a slight mound.
Halve each bacon slice crosswise. Wrap one half-slice around the center of each stuffed jalapeño, allowing a slight overlap. Arrange seam-side down on the prepared baking sheet.
Bake for 20-25 minutes, until the bacon is crispy and the filling is hot and bubbly. For crispier bacon, broil for the last 2-3 minutes, watching closely.
Allow the poppers to rest on the baking sheet for about 5 minutes before handling.
Move to a serving platter, top with chopped chives or green onions if desired, and serve warm with extra ranch or blue cheese dressing for dipping.