Here are recent FE pass rates for all ABET examinees. First, find out whether your state or school requires you to take the exam for your major or working discipline.
Some states do.
If not, the choice is yours. The advantage of taking the General exam is that you have to study all the same subject areas anyway to prepare for the morning session. Many engineers, however, will be most comfortable taking the DS afternoon exam that focuses on their own field. The following table allows comparison of the pass rates of engineers who took the DS exam in their field versus those in the same discipline who took the General exam.