I would get the IMAX version. Anyone that saw The Dark Knight's tunnel/highway/tumbler chase scene will know why.
But for those that don't, that scene was shot in IMAX. I saw the movie in a non-IMAX theater. When that scene played, you could tell when the tumbler crashes into the garbage truck that there should be more picture, but it was cropped to fit widescreen so there was this awkward moment where the camera appeared too close but it really wasn't because the picture was cropped.
Look at it this way: with the IMAX version, you'll see the entire shot whereas with the wide screen version, they'll crop the IMAX shots and you may miss some little things or have an awkward moment. I saw the wide screen version, and I thought during the forest fight after Optimus said "I'll take you all on" when the camera panned to Sam on the ground before panning back up to Optimus was an awkward moment. It was like they did that deliberately to let you know he was there. It seemed to me that perhaps Sam and Optimus were in the same shot on IMAX, but because they cropped it for widescreen they had to pan down to show Sam. Thus we miss a little of the fight. Perhaps the IMAX version will have no pan since it shows the entire shot?
I am EXTREMELY anal about missing parts of the picture, so I would get the IMAX. It's why I buy widescreen over the full screen TV versions, where they crop the widescreen picture to fit a standard TV screen.
Kind of ironic to crop IMAX to fit widescreen, since IMAX uses standard TV screen ratios. Widescreen gets cropped for standard TV and IMAX gets cropped for widescreen.
tldr: GET IMAX.