I don't know about the most common, but I've used Ansys with Solidworks, and it is a nice interface. One of the key things to me (from my standpoint as a Design Engineer, others may disagree) about a good interface between CAD and FEA is the ability to parameterize geometry in the FEA software, so that you can quickly analyze different versions of a part while trying to optimize your design. (For example, changing the diameter or length of a part.)
You don't get that type of thing with STEP and parasolid importion, and you have to reapply all of your Boundary Conditions and other settings each time you import a new part.
Just my 2 cents.