Upload STEP or IGES?

From my humble experience, I've never had a problem with Parasolid and always prefer to use it for it's reliability, faster exporting and importing, and much much smaller file size but it seems not all CAD packages support it, STEP and IGES are more widely supported.
STEP is much better for solids and I don't use IGES unless I'm having problems with exporting surfaces as STEP.
In the end, all of them support face properties (colors) and if you test it and it imports fine then use it.
I made a research some time ago but I lost it.

Hi Aaron
Hardi has took the time to explain
what these files are @
http://grabcad.com/questions/step-slash-iges-files
this should answer your question.

Since I'm only using SW(2010), from personal experience, STEP files suit me much more than IGES. So far, had no problems with *.stp files, not so lucky with *.igs. I have no knowledge about how ADInventor and other software copes with parasolid (*.x_t) files, but they do work well in SW, so, this is probably a matter of being willing to create several versions of the same file and upload them either all, or prepare them and upload at request. I have no problem with that by any means, made a separate folder of all files I uploaded to GrabCAD... So, if anyone needs a different version of any of the files I uploaded, just drop me a line and I'll upload a version of your choice ;)