2d6 + action value vs. 8 + difficulty value
In Bulletproof Blues third edition (currently under construction), all rolls are opposed:
2d6 + action value vs. 2d6 + difficulty value
Why? Three reasons.
First, new players often forgot the “8” in “8 + difficulty value”, and would need to look it up. Having to look things up is no fun.
Second, when on the receiving end of an attack, players like to feel that they have some influence on the outcome. Although it makes little difference statistically, players feel more involved if they get to roll some dice when their character is attacked.