You're probably better off doing passage practice if you're not familiar with the format.
But don't discount discrete questions; you'll see them on Test day as well.
So a mixture of both? With preferably more passage-based ones obviously. Try the TPR Science Workbook. It might be what you're looking for.
The discrete (freestanding) questions tend to be the types of questions most people are more familiar with. They are the "plug and chug" standard undergrad exam-type questions.
The passage questions tend to be more difficult just because they're foreign to most people, so they require more practice.