I've used AutoCAD thru '04, MasterCam, Microstation J, Inventor, and Wildfire. How well one works over another is, in my opinion, largely influenced by ones ability to visualize. Everyone is different and one software may better suit one persons thought processes than another. My only opinion is that the transition from AutoCAD to Pro-E was quite easy. Inventor is difficult to use to me. MasterCam V.9 is fast and efficient for CNC work. Microstation J smokes through P&ID's. I would like to try UG and Solidworks. Other than that, to each, his own.