If we consider the power levels, Majin Vegeta is far stronger physically. But Bulma is known for her quick thinking and resourcefulness. In a fanfiction, the writer could make it so that Bulma finds a way to temporarily disable Majin Vegeta, like using some sort of device that disrupts the Majin energy. But if it goes on for a long time, Majin Vegeta's power and fighting experience would likely prevail. So, while Bulma could put up a good fight, Majin Vegeta is more likely to be the victor in the end.
Majin Vegeta would be the likely victor in a physical confrontation. He has superhuman strength, speed, and combat abilities that Bulma simply doesn't possess. But if the fight was more about strategy and using resources, Bulma might be able to hold her own. For example, if she had time to set up some sort of technological trap, she could potentially incapacitate Majin Vegeta. Still, overall, given his raw power, Majin Vegeta has the edge.
It's really hard to say. Majin Vegeta is an extremely powerful Saiyan with enhanced strength. But Bulma is no pushover. She's intelligent and could potentially use her intellect to outwit him. However, in a straight - up physical fight, Majin Vegeta would probably be the victor. But if it's a fight that involves more than just physical strength, like a battle of wits and using the environment, Bulma could have a chance.