US history is the easiest among all histories and has the shortest syllabus. That is why people have scored more in it. However, this does not mean that you will score high in it.
Your score is dependent upon the following things:
a. your preparation and grip on the subject
b. your style of expression (how you answer questions)
c. your ability to reason based on the nature of questions asked

All these elements will become part of you if and only if you feel that you are enjoying studying the subject. Don't go with trends, go with your gut. If you went with trends, you would start considering some subjects (such as English Literature) undoable.

Take a deep breath, look at all the possible options (based on your interest and length of syllabus), and then choose what's best for you.

Best of luck!!!