[Andy A.]

The most successful file format I've had experience with is the .stp or .step format. It does transfer solid body info between inventor and solidworks very well. You won't have access to anything like the list of functions used to construct the model in it's original program though.

Think of it as the .txt format of parametric modeling.

Also, I wouldn't bother saving assemblies as .stp. My guess is that constraints do not carry over well, if at all. Save individual parts and reconstruct assemblies in the new program.

-Andy A.