I have and enjoy both.
Depends on what kind of game you want, SW is quite complex, lots of modes, stacking modes, moving around multipliers - and a much better theme. IM although SW is super fast and flow-ey, IM has more shots and is just a great fun shooting pin, code depth is medium, still great for home use, just not as complex as SW.
Try both, some guys cant handle the music on IM, I like the art, callouts, music and lighting on both.
If I had to choose, I'd pick IM but keep in mind I've owned SW a year longer so its not as 'new'