AutoCAD vs. ProEng.
Prior to the ACAD "Inventor" product, AutoCad was basically a 2D drafting board. But its beauty is its ease of use and immediate feedback re: any errors of entry. Now, though I haven't used it, I understand that Inventor is full 3D and takes only a day to learn how to use.
My problem with Pro/E is the steep learning curve (takes weeks to learn to use well) and you can get a dozen steps in, then try to "Regenerate" or proceed and you get this "fatal error" message. Then, you spend the rest of the day trying to figure out what you did wrong. Also, PTC (maker of Pro/E) keeps changing the GUI methodology, and they are about to come out with a new, sweeping change. So for an experienced user, it's like starting over.
A person who used AutoCad 10 years ago can still use it today, albeit "the old way."
As with most software, there will be continued merging and consolidation of method and capability. 10 years from now, AutoDesk will by PTC or vise-versa, and there will be one standard product. Or.............. just like PTC did, somebody will come along and say none of these products combines capability with ease of use (look at Solid Edge today because some people claim they have already achieved this goal) and they will create it from the ground up and blow the competition away. Wolfram Research could probably do this if they decided to enter the CAD/CAE market, but I'm not sure they will.
I DON'T LIKE Pro/E because it is a pain in the but to use, the learning curve takes forever and just when you learn it, they change it.