There is a very long thread here recently on STL vs STEP. If you want the long version and have a few hours, read this.
To spare you the wall of words, let me simplify.
- STL files are a mesh of triangles
- STEP files are geometric descriptions of geometric shapes such as lines, circles, arcs and angles. They are far more accurate and Slicers support them as well as STL.
- After a STEP file is imported into a slicer, the model is converted into a mesh and all geometry data is lost.
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So when I say import with the lowest version, that’s only if your CAD supports versions. There are three versions. STEP AP203, AP214 and AP242. AP203 is the earliest and oldest and will not contain the same complex data that later versions might hold. Thus allowing for less information to be processed by the slicer.
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STEP files and STL files in a text editor can look remarkably similar but there are very stark differences. STEP is covered under ISO 10303-21 and was designed specifically for CAD portability. It’s predecessor was IGES. STL was designed by 3D Labs specifically for 3D printing.
In the world you’re trying to live in, CAD 
FDM, mastering the concepts between the two formats will help you develop a more intuitive understanding of what will and will not work in a 3D printing or CAD use-case. You don’t need to be an expert to get the feel of which file format performs in a specific manner. In fact, you can know nothing about the file syntax so long as you wrap your mind around the differences between a parametric geometry and a mesh. It’s been demonstrated in this forum that many who believe they understand the concepts actually do not.