Bribery or anything else that affects their lawmaking decisions is significantly worse because the impact is so much larger.
But there is a third option: They are making decisions based on what will move something the most - doesn't matter what, and doesn't matter which way, and doesn't matter for how long. Then they invest in that thing a bit before the decision becomes public that moves that thing.
Don't get me wrong, I think campaign donations or even more explicit bribes are a huge problem, too, but it is already insane to me that you would ban and prosecute "ordinary insider traders" and just let lawmakers do whatever. If presidents have to give up peanut farming, then asking for congressmembers to be utterly decoupled from stock trading decisions is only fair and sensible in my view.