WDR is usually better when there's likely to be a lot of variation in the lighting across the field of view, as it takes the entire image into account when it does the corrections.
BLC uses a smaller area for exposure control, so changes outside that area won't affect it. Typically, BLC is used where you need good exposure in one area, like a door coming into a shop with sunlight coming in the windows around the door. It'll expose for the door, and ignore the other areas. If you wanted to expose the dark top area and ignore the bottom area, BLC would do that.
Hik's BLC isn't great, as it just gives you a general area description and doesn't show what area it's using (at least on the version I'm using). Most cams let you draw a box around the area you want to use BLC on.