Personally, I prefer not to know the DC in a tabletop game, but the relative difficulty can often be ascertained based on questioning the attitude of whoever you're talking to, which is more difficult to do in a video game.
If I were going to change one thing about how dialog checks work, I would remove the skill name from the dialog choices. I want to say the thing that makes the most sense for my character, not automatically lean on the skill that I'm strongest with.
