I assume both is not an option?
I went from 2011 335 sedan to the 35i X3. I like the visibility, space and overall function of the X3. The 335 was a blast to drive, but putting people and stuff in it was always a challenge. With the X3, people and stuff pop right in and away we go. I still have the N55 engine and sport mode when I want to get frisky. I certainly don't regret the X3 purchase over the 335 at all.
If you go with the X3, get the dynamic handling package, get the dynamic handling package, get the dynamic handling package! It makes the ride so much better in each setting. For $1400, it is a real bargain. BMW has this technology down and I'm not sure I would consider another car if it didn't have this capability.